Resin, resist composition and method for producing resist pattern

ABSTRACT

A resist composition includes (A1) a resin which includes a structural unit represented by formula (a4), and a structural unit having an adamantane lactone group, and the resin has no acid-labile group, (A2) a resin having an acid-labile group, and an acid generator. 
                         
In the formula (a4), R 3  represents a hydrogen atom or a methyl group, and R 4  represents a C 1  to C 24  saturated hydrocarbon group having a fluorine atom, and a methylene group of the saturated hydrocarbon group may be replaced by an oxygen atom or a carbonyl group.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to Japanese Application No. 2014-187412 filed on Sep. 16, 2014. The entire disclosures of Japanese Application No. 2014-187412 is incorporated hereinto by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The disclosure relates to a resin, a resist composition and a method for producing resist pattern.

2. Related Art

A resist composition including a resin having a combination of structural units below, a resin having an acid-labile group and an acid generator is described in Patent document of JP2014-41346A.

A resist composition including a resin having a combination of structural units below, a resin having an acid-labile group and an acid generator is described in Patent document of JP200888343A.

SUMMARY OF THE INVENTION

The disclosure provides following inventions of <1> to <13>.

<1> A resist composition includes

(A1) a resin which includes a structural unit represented by formula (a4):

wherein R³ represents a hydrogen atom or a methyl group, and

R⁴ represents a C₁ to C₂₄ saturated hydrocarbon group having a fluorine atom, and a methylene group of the saturated hydrocarbon group may be replaced by an oxygen atom or a carbonyl group,

and a structural unit having an adamantane lactone group, and

the resin having no acid-labile group,

(A2) a resin having an acid-labile group, and

an acid generator.

<2> The resist composition according to <1>, wherein

the structural unit having an adamantane lactone group is a structural unit represented by formula (a3-4I):

wherein R⁵ represents a hydrogen atom, a halogen atom, or a C₁ to C₆ alkyl group that may have a fluorine atom,

A⁴ represents an oxygen atom or an NH group, and

A⁵ represents a single bond or a C₁ to C₈ alkanediyl group where a methylene group may be replaced by an oxygen atom or a carbonyl group.

<3> The resist composition according to <1> or <2>, wherein

the structural unit having an adamantane lactone group is a structural unit represented by formula (a3-4′):

wherein R⁵ represents a hydrogen atom, a halogen atom, or a C₁ to C₆ alkyl group that may have a fluorine atom, and

A¹ represents a single bond, *-A²-O—, *-A²-CO—O—, *-A²-CO—O-A³-CO—O— or *-A²-O—CO-A³-O— where * represents a binding site to an oxygen atom, and A² and A³ each independently represent a C₁ to C₆ alkanediyl group.

<4> The resist composition according to claim 1, wherein

the resin (A1) further includes a structural unit represented by formula (I):

wherein R¹ represents a hydrogen atom or a methyl group, and

L¹ represents a single bond or a C₁ to C₁₈ divalent saturated hydrocarbon group where a methylene group may be replaced by an oxygen atom or a carbonyl group, and

R² represents a C₃ to C₁₈ alicyclic hydrocarbon group where a hydrogen atom may be replaced by a C₁ to C₈ aliphatic hydrocarbon group or a hydroxy group, provided that the carbon atom directly bonded to L¹ has no aliphatic hydrocarbon group by which a hydrogen atom has been replaced.

<5> The resist composition according to <4>, wherein

R² is an unsubstituted C₃ to C₁₈ alicyclic hydrocarbon group.

<6> The resist composition according to any one of <1> to <5>, wherein

the structural unit represented by the formula (a4) is at least one structural unit selected from the group consisting of a structural unit represented by formula (a4-0), a structural unit represented by formula (a4-1), a structural unit represented by formula (a4-2) and a structural unit represented by formula (a4-3):

wherein R^(f1) represents a hydrogen atom or a methyl group, and

R^(f2) represents a C₁ to C₂₀ saturated hydrocarbon group having a fluorine atom;

wherein R^(f3) represents a hydrogen atom or a methyl group,

L³ represents a C₁ to C₁₈ divalent saturated hydrocarbon group where a methylene group may be replaced by an oxygen atom or a carbonyl group, and

R^(f4) represents a C₁ to C₂₀ saturated hydrocarbon group having a fluorine atom;

wherein R^(f5) represents a hydrogen atom or a methyl group,

L⁴ represents a C₁ to C₁₈ divalent saturated hydrocarbon group where a methylene group may be replaced by an oxygen atom or a carbonyl group, and

R^(f6) represents a C₁ to C₂₀ saturated hydrocarbon group having a fluorine atom;

wherein R^(f7) represents a hydrogen atom or a methyl group,

L⁵ represent a C₁ to C₆ alkanediyl group,

A^(f13) represents a C₁ to C₁₈ divalent saturated hydrocarbon group that may have a fluorine atom,

X^(f12) represents an oxycarbonyl group or a carbonyloxy group, and

A^(f14) represents a C₁ to C₁₇ saturated hydrocarbon group that may have a fluorine atom,

provided that at least one of A^(f13) and A^(f14) represents a saturated hydrocarbon group having a fluorine atom.

<7> The resist composition according to any one of <3 to <6>, wherein

the structural unit represented by the formula (a3-4′) has an adamantane lactone group represented by formula (a3-4II-a) or formula (a3-4II-b)::

wherein * represents a binding site to A¹.

<8> The resist composition according to any one of <1> to <7>, wherein

the resin (A2) includes a structural unit selected from the group consisting of a structural unit represented by formula (a1-1) and a structural unit represented by formula (a1-2):

wherein L^(a1) and L^(a2) independently represent —O— or *—O—(CH₂)_(k1)—CO—O—,

k1 represents an integer of 1 to 7,

* represents a binding site to —CO—,

R^(a4) and R^(a5) each independently represent a hydrogen atom or a methyl group,

R^(a6) and R^(a7) each independently represent a C₁ to C₈ alkyl group, a C₃ to C₁₈ alicyclic hydrocarbon group or a combination thereof,

m1 represents an integer of 0 to 14,

n1 represents an integer of 0 to 10, and

n1′ represents an integer of 0 to 3.

<9> The resist composition according to <8>, wherein

the resin (A2) includes a structural unit represented by formula (a1-1) and a structural unit represented by formula (a1-2).

<10> A method for producing a resist pattern includes steps (1) to (5);

(1) applying the resist composition according to any one of <1> to <9> onto a substrate;

(2) drying the applied composition to form a composition layer;

(3) exposing the composition layer;

(4) heating the exposed composition layer, and

(5) developing the heated composition layer.

<11> A resin includes

a structural unit represented by formula (a4):

wherein R³ represents a hydrogen atom or a methyl group,

R⁴ represents a C₁ to C₂₄ saturated hydrocarbon group having a fluorine atom, a methylene group of the saturated hydrocarbon group may be replaced by an oxygen atom or a carbonyl group and

a structural unit having an adamantane lactone group,

the resin having no acid-labile group.

<12> The resin according to <11>, wherein

the structural unit having an adamantane lactone group is a structural unit represented by formula (a3-4I):

wherein R⁵ represents a hydrogen atom, a halogen atom, or a C₁ to C₆ alkyl group that may have a fluorine atom,

A⁴ represents an oxygen atom or an NH group, and

A⁵ represents a single bond or a C₁ to C₈ alkanediyl group where a methylene group may be replaced by an oxygen atom or a carbonyl group.

<13> The resin according to <11> or <12>, wherein

the structural unit having an adamantane lactone group is a structural unit represented by formula (a3-4′):

wherein R⁵ represents a hydrogen atom, a halogen atom, or a C₁ to C₆ alkyl group that may have a fluorine atom, and

A¹ represents a single bond, *-A²-O—, *-A²-CO—O—, *-A²-CO—O-A³-CO—O— or *-A²-O—CO-A³-O— where * represents a binding site to an oxygen atom, and A² and A³ each independently represent a C₁ to C₆ alkanediyl group.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

“(Meth)acrylic monomer” means a monomer having a structure of “CH₂═CH—CO—” or “CH₂═C(CH₃)—CO—”, as well as “(meth)acrylate” and “(meth)acrylic acid” mean “an acrylate or methacrylate” and “an acrylic acid or methacrylic acid,” respectively. Herein, chain structure groups include those having a linear structure and those having a branched structure. The indefinite articles “a” and “an” are taken as the same meaning as “one or more”.

In the specification, the term “solid components” means components other than solvents in a resist composition.

<Resin>

The resin of the disclosure, which is sometimes referred to as “resin (A1)”, includes a structural unit represented by formula (a4) as described later and a structural unit having an adamantane lactone group, while the resin has no acid-labile group.

The resin is usable for resist compositions including that of the disclosure.

The resin (A1) may further include a structural unit represented by formula (I) as described later.

The resin (A1) preferably consists of the structural unit represented by formula (a4), and a structural unit having an adamantane lactone group, or consists of the structural unit represented by formula (a4), a structural unit having an adamantane lactone group, and a structural unit represented by formula (I).

<Resist Composition>

The resist composition of the disclosure includes

the resin (A1),

a resin which has an acid-labile group (which resin is sometimes referred to as “resin (A2)”), and

an acid generator.

Here the “acid-labile group” means a group having a leaving group capable of detaching by contacting with an acid to thereby form a hydrophilic group such as a hydroxy or carboxy group.

The resist composition preferably includes a quencher (which is sometimes referred to as “quencher (C)”) and/or a solvent (which is sometimes referred to as “solvent (E)”) in addition to the resins (A1) and (A2), and the acid generator. Further, the resist composition may include a resin other than the resin (A1) and resin (A2) (which is sometimes referred to as “resin (X)”).

<Resin (A1)>

The resin (A1) includes a structural unit represented by formula (a4) (which is sometimes referred to as “structural unit (a4)”):

wherein R³ represents a hydrogen atom or a methyl group, and

R⁴ represents a C₁ to C₂₄ saturated hydrocarbon group having a fluorine atom, and a methylene group contained in the saturated hydrocarbon group may be replaced by an oxygen atom or a carbonyl group.

Examples of the saturated hydrocarbon group having a fluorine atom of R⁴ include a fluorinated alkyl group such as difluoromethyl, trifluoromethyl, 1,1-difluoroethyl, 2,2-difluoroethyl, 2,2,2-trifluoroethyl, perfluoroethyl, 1,1,2,2-tetrafluoropropyl, 1,1,2,2,3,3-hexafluoropropyl, perfluoroethylmethyl, 1-(trifluoromethyl)-1,2,2,2-tetrafluoroethyl, 1-(trifluoromethyl)-2,2,2-trifluoroethyl, perfluoropropyl, 1,1,2,2-tetrafluorobutyl, 1,1,2,2,3,3-hexafluorobutyl, 1,1,2,2,3,3,4,4-octafluorobutyl, perfluorobutyl, 1,1-bis(trifluoromethyl)methyl-2,2,2-trifluoroethyl, 2-(perfluoropropyl)ethyl, 1,1,2,2,3,3,4,4-octafluoropentyl, perfluoropentyl, 1, 1,2,2,3,3,4,4,5,5-decafluoroentyl, 1,1-bis(trifluoromethyl)2,2,3,3,3-pentafluoropropyl, 2-(perfluorobutyl)ethyl, 1,1,2,2,3,3,4,4,5,5-decafluorohexyl, 1,1,2,2,3,3,4,4,5,5,6,6-dodecafluorohexyl, perfluoropentylmethyl and perfluorohexyl groups; and

a fluorinated cycloalkyl group such as perfluorocyclohexyl and perfluoroadamantyl groups.

The structural unit (a4) is preferably a structural unit represented by formula (a4-0), a structural unit represented by formula (a4-1), a structural unit represented by formula (a4-2), and a structural unit represented by formula (a4-3) described later, more preferably the structural unit represented by formula (a4-0), the structural unit represented by formula (a4-1) and the structural unit represented by formula (a4-2), still more preferably the structural unit represented by formula (a4-0).

Hereinafter, the structural unit represented by formula (a4-0), the structural unit represented by formula (a4-1), the structural unit represented by formula (a4-2), and the structural unit represented by formula (a4-3) are sometimes referred to as “the structural unit (a4-0), “the structural unit (a4-1)”, “the structural unit (a4-2)”, and “the structural unit (a4-3)”, respectively.

In the formula (a4-0), R^(f1) represents a hydrogen atom or a methyl group, and

R^(f2) represents a C₁ to C₂₀ saturated hydrocarbon group having a fluorine atom.

In the formula (a4-1), R^(f3) represents a hydrogen atom or a methyl group,

L³ represents a C₁ to C₁₈ divalent saturated hydrocarbon group where a methylene group may be replaced by an oxygen atom or a carbonyl group, and

R^(f4) represents a C₁ to C₂₀ saturated hydrocarbon group having a fluorine atom.

The total carbon number contained in the group of L³ and R^(f4) is preferably 21 or less. The total carbon number of the group includes the number of the carbon atom replaced by an oxygen atom or a carbonyl group.

In the formula (a4-2), R^(f5) represents a hydrogen atom or a methyl group,

L⁴ represents a C₁ to C₁₈ divalent saturated hydrocarbon group where a methylene group may be replaced by an oxygen atom or a carbonyl group, and

R^(f6) represents a C₁ to C₂₀ saturated hydrocarbon group having a fluorine atom.

The total carbon number contained in the group of L⁴ and R^(f6) is preferably 21 or less.

In the formula (a4-1) and the formula (a4-2), examples of the divalent saturated hydrocarbon group of L³ and L⁴ include a saturated aliphatic hydrocarbon group and a saturated alicyclic hydrocarbon group, and a saturated aliphatic hydrocarbon group is preferred.

Examples of the saturated aliphatic hydrocarbon group include an alkanediyl such as methylene, ethylene, propanediyl, butanediyl and pentanediyl.

Examples of the saturated alicyclic hydrocarbon group include any of a monocyclic group and a polycyclic group. Examples of the monocyclic group include cycloalkanediyl group such as cyclopentanediyl and cyclohexanediyl groups. Examples of the polycyclic group include adamantanediyl and norbornanediyl groups.

Examples of the saturated hydrocarbon group in which a methylene group has been replaced by an oxygen atom or a carbonyl group include groups represented by formula (L3-1) to formula (L3-3). In the formula (L3-1) to the formula (L3-3), * represents a binding site to an oxygen atom.

In the formulae, X₃ ^(X1) represents an oxycarbonyl group or a carbonyloxy group,

L₃ ^(X1) represents a C₁ to C₁₆ divalent saturated aliphatic hydrocarbon group,

L₃ ^(X2) represents a single bond or a C₁ to C₁₅ divalent saturated aliphatic hydrocarbon group,

provided that the total carbon number contained in the group of L₃ ^(X1) and L₃ ^(X2) is 16 or less;

L₃ ^(X3) represents a single bond or a C₁ to C₁₇ divalent saturated aliphatic hydrocarbon group,

L₃ ^(X4) represents a single bond or a C₁ to C₁₆ divalent saturated aliphatic hydrocarbon group,

provided that the total carbon number contained in the group of L₃ ^(X3) and L₃ ^(X4) is 17 or less;

L₃ ^(X5) represents a C₁ to C₁₅ divalent saturated aliphatic hydrocarbon group,

L₃ ^(X6) and L₃ ^(X7) each independently represent a single bond or a C₁ to C₁₄ divalent saturated aliphatic hydrocarbon group,

provided that the total carbon number contained in the group of L₃ ^(X5), L₃ ^(X6) and L₃ ^(X7) is 15 or less.

L₃ ^(X1) is preferably a C₁ to C₈ divalent saturated aliphatic hydrocarbon group, and more preferably methylene or ethylene group.

L₃ ^(X2) is preferably a C₁ to C₈ divalent saturated aliphatic hydrocarbon group, and more preferably methylene or ethylene group.

L₃ ^(X3) is preferably a C₁ to C₈ divalent saturated aliphatic hydrocarbon group.

L₃ ^(X4) is preferably a C₁ to C₈ divalent saturated aliphatic hydrocarbon group.

L₃ ^(X5) is preferably a C₁ to C₈ divalent saturated aliphatic hydrocarbon group, and more preferably methylene or ethylene group.

L₃ ^(X6) is preferably a C₁ to C₈ divalent saturated aliphatic hydrocarbon group, and more preferably methylene or ethylene group.

L₃ ^(X7) is preferably a C₁ to C₈ divalent saturated aliphatic hydrocarbon group.

Examples of the group represented by the formula (L3-1) include the following ones.

Examples of the group represented by the formula (L3-2) include the following ones.

Examples of the group represented by the formula (L3-3) include the following ones.

L³ and L⁴ are preferably methylene group or ethylene group.

Examples of the saturated hydrocarbon group having a fluorine atom include the same examples as those referring to the group of R⁴ in the formula (a4).

Examples of the structural unit (a4-0) include the following ones.

Examples of the structural unit (a4-0) include those in which a methyl group corresponding to R^(f1) has been replaced by a hydrogen atom in the structural units represented by the above formulae.

Examples of the structural unit (a4-1) include the following ones.

Examples of the structural unit (a4-1) include those in which a methyl group corresponding to R^(f3) has been replaced by a hydrogen atom in the structural units represented by the above formulae.

Examples of the structural unit (a4-2) include the following ones.

Examples of the structural unit (a4-2) include those in which a methyl group corresponding to R^(f5) has been replaced by a hydrogen atom in the structural units represented by the above formulae.

Examples of the structural unit (a4) include a structural unit presented by the formula (a4-3) (which is sometimes referred to as “structural unit (a4-3)”):

wherein R^(f7) represents a hydrogen atom or a methyl group,

L⁵ represent a C₁ to C₆ alkanediyl group,

A^(f13) represents a C₁ to C₁₈ divalent saturated hydrocarbon group that may have a fluorine atom,

X^(f12) represents an oxycarbonyl group or a carbonyloxy group, and

A^(f14) represents a C₁ to C₁₇ saturated hydrocarbon group that may have a fluorine atom,

provided that at least one of A^(f13) and A^(f14) represents a saturated hydrocarbon group having a fluorine atom.

In the formula (a4-3), the total carbon number contained in the group of L⁵, A^(f13) and A^(f14) is preferably 20 or less.

Examples of the alkanediyl group of L⁵ include a chain alkanediyl group such as methylene, ethylene, propane-1,3-diyl, butane-1,4-diyl, pentane-1,5-diyl and hexane-1,6-diyl groups;

a branched alkanediyl group such as 1-methylpropane-1,3-diyl, 2-methylpropane-1,3-diyl, 2-methylpropane-1,2-diyl, 1-methylbutane-1,4-diyl and 2-methylbutane-1,4-diyl groups.

Examples of the divalent saturated hydrocarbon group of A^(f13) include any of a saturated aliphatic hydrocarbon group, a saturated alicyclic hydrocarbon group, or a combination thereof. The aliphatic hydrocarbon group may have a carbon-carbon unsaturated bond, and is preferably a saturated aliphatic hydrocarbon group.

The saturated hydrocarbon group that may have a fluorine atom of A^(f13) is preferably the saturated aliphatic hydrocarbon group that may have a fluorine atom, and preferably a perfuloroalkandiyl group.

Examples of the divalent saturated aliphatic hydrocarbon that may have a fluorine atom include an alkanediyl group such as methylene, ethylene, propanediyl, butanediyl and pentanediyl groups; a perfluoroalkanediyl group such as difluoromethylene, perfluoroethylene, perfluoropropanediyl, perfluorobutanediyl and perfluoropentanediyl groups.

The divalent saturated alicyclic hydrocarbon group that may have a fluorine atom is any of a monocyclic or a polycyclic group.

Examples of the monocyclic group include cyclohexanediyl and perfluorocyclohexanediyl groups.

Examples of the polycyclic group include adamantanediyl, norbornanediyl, and perfluoroadamantanediyl groups.

Examples of the saturated hydrocarbon group of A^(f14) include any of a saturated aliphatic hydrocarbon group, a saturated alicyclic hydrocarbon group, or a combination thereof. The aliphatic hydrocarbon group may have a carbon-carbon unsaturated bond, and is preferably a saturated aliphatic hydrocarbon group.

Examples of the saturated aliphatic hydrocarbon group that may have a halogen atom include trifluoromethyl, difluoromethyl, methyl, perfluoromethyl, 1,1,1-trifluoroethyl, 1,1,2,2-tetrafluoroethyl, ethyl, perfluoropropyl, 1,1,1,2,2-pentafluoropropyl, propyl, perfluorobutyl, 1,1,2,2,3,3,4,4-octafluorobutyl, butyl, perfluoropentyl, 1,1,1,2,2,3,3,4,4-nonafluoropentyl, pentyl, hexyl, perfluorohexyl, hepthyl, perfluoroheptyl, octyl and perfluorooctyl groups.

The saturated cyclic aliphatic hydrocarbon group that may have a fluorine atom is any of monocyclic or polycyclic group. Examples of the monocyclic group include cyclopropylmethyl, cyclopropyl, cyclobutylmethyl, cyclopentyl, cyclohexyl and perfluorocyclohexyl groups. Examples of the polycyclic group include adamantyl, norbornyl and perfluoroadamantyl groups

Examples of the combination of the saturated aliphatic hydrocarbon group and saturated alicyclic hydrocarbon group include adamantylmethyl, norbornylmethyl, and perfluoroadamantylmethyl groups

In the formula (a4-3), L⁵ is preferably an ethylene group.

The saturated aliphatic hydrocarbon group of A^(f13) is preferably a C₁ to C₆ aliphatic hydrocarbon group, more preferably a C₂ to C₃ aliphatic hydrocarbon group.

The saturated hydrocarbon group of A^(f14) is preferably a C₃ to C₁₂ saturated hydrocarbon group, more preferably a C₃ to C₁₀ hydrocarbon group. Among these, A^(f14) is preferably a group containing a C₃ to C₁₂ alicyclic hydrocarbon group, more preferably a cyclopropylmethyl, cyclopentyl, cyclohexyl, norbornyl or adamantyl group.

Examples of the structural unit (a4-3) include the following ones.

Examples of the structural unit (a4-3) include those in which a methyl group corresponding to R^(f7) has been replaced by a hydrogen atom in the structural units represented by the above formulae.

The structural unit (a4-0) is derived from a compound represented by formula (a4′-0) (which is sometimes referred to as “compound (a4′-0)”):

wherein R^(f1) and R^(f2) are as defined above.

As the compound (a4′-0), a marketed product or a compound which is produced by a known method may be used.

The known method includes a method in which (meth)acrylic acid or derivatives thereof, for example, (meth)acrylic chloride is condensed with a suitable alcohol (HO—R^(f2)). The marketed product is the following ones.

The structural unit (a4-1) is derived from a compound represented by formula (a4′-1) (which is sometimes referred to as “compound (a4′-1)”):

wherein R^(f3), R^(f4) and L³ are as defined above.

The compound (a4′-1) can be produced by reacting a compound represented by formula (a4′-1-1) with a compound represented by formula (a4′-1-2) in the presence of a basic catalyst in a solvent:

wherein R^(f3), R^(f4) and L³ are as defined above.

Preferred examples of the solvent include tetrahydrofuran.

Preferred examples of the basic catalyst include pyridine.

Examples of the compound represented by the formula (a4′-1-1) include hydroxyethylmethacrylate, which is available on the market. Also, a compound which is produced by a known method including a method in which (meth)acrylic acid or derivatives thereof, for example, (meth)acrylic chloride is condensed with a suitable diol (HO-L³-OH), can be used.

As the compound represented by the formula (a4′-1-2), an anhydrate that has been converted from an appropriate caroboxylic acid in accordance with R^(f4) can be used. Examples of the marketed product include heptafluorobutyric anhydride.

The structural unit (a4-2) is derived from a compound represented by formula (a4′-2) (which is sometimes referred to as “compound (a4′-2)”):

wherein R^(f5), R^(f6) and L⁴ are as defined above.

The compound (a4′-2) can be produced by reacting a compound represented by formula (a4′-2-1) with a compound represented by formula (a4′-2-2) in the presence of a catalyst in a solvent:

wherein R^(f6), R³ and L⁴ are as defined above.

Preferred examples of the solvent include dimethylformamide.

Preferred examples of the catalyst include potassium carbonate and potassium iodide.

Preferred examples of the compound represented by the formula (a4′-2-1) include a methacrylic acid, which is available on the market.

The compound represented by the formula (a4′-2-2) can be produced by reacting a compound represented by formula (a4′-2-3) with a compound represented by formula (a4′-2-4) in the presence of a basic catalyst in a solvent:

wherein R^(f6) and L⁴ are as defined above.

Preferred examples of the solvent include tetrahydrofuran.

Preferred examples of the basic catalyst include pyridine.

As the compound represented by the formula (a4′-2-3), a compound in accordance with R^(f4) can be used. When chloroacetyl chloride is used as the compound represented by the formula (a4′-2-3), a compound represented by the formula (a4′-2-2) in which L⁴ is methyl group can be produced. Chloroacetyl chloride is available on the market.

As the compound represented by the formula (a4′-2-4), an alcohol in accordance with R^(f6) can be used. When 2,2,3,3,4,4,4-heptafluoro-1-butanol is used as the compound represented by the formula (a4′-2-4), a compound represented by the formula (a4′-2-2) in which R^(f6) is an aliphatic hydrocarbon group has been substituted with fluorine atom can be produced. 2,2,3,3,4,4,4-Heptafluoro-1-butanol is available on the market.

The structural unit (a4-3) is derived from a compound represented by formula (a4′-3) (which is sometimes referred to as “compound (a4′-3)”):

wherein R^(f7), L⁵, A^(f13), X^(f12) and A^(f14) are as defined above.

The compound represented by the formula (a4′-3) can be produced by reacting a compound represented by the formula (a4′-3-1) with a carboxylic acid represented by the formula (a4′-3-2). This reaction is generally carried out in a solvent:

wherein R^(f7), L⁵, A^(f13), X^(f12) and A^(f14) are as defined above.

Preferred examples of the solvent include tetrahydrofuran and toluene.

As the compound represented by the formula (a4′-3-1), a marketed product or a compound which is produced by a known method may be used.

The known method includes a method in which (meth)acrylic acid or derivatives thereof, for example, (meth)acrylic chloride is condensed with a suitable diol (HO-L⁵-OH). Examples of the marketed product include hydroxyethyl methacrylate.

The compound represented by the formula (a4′-3-2) can be produced by a known method. Examples thereof include the following ones.

The resin (A1) includes the structural unit having an adamantane lactone group. The structural unit having an adamantane lactone group further includes a polymerizable group in addition to an adamantane lactone group. Examples of the polymerizable group include a vinyl group, an acryloyl group, a methacryloyl group, an acryloyloxy group, a methacryloyloxy group, an acryloylamino group and a methacryloylamino group, and preferably a vinyl group, an acryloyl group and a methacryloyl group.

The structural unit having an adamantane lactone group may has a structure represented by formula (a3-4I′):

wherein R⁵ represents a C₁ to C₆ alkyl group that may have a halogen atom, a hydrogen atom or a halogen atom,

A⁴ represents an oxygen atom or an NH group,

A⁵ represents a single bond or a C₁ to C₈ alkanediyl group where a methylene group may be replaced by an oxygen atom or a carbonyl group, and

* represents a binding site to a moiety having an adamantane lactone.

Examples of the halogen atom include fluorine, chlorine, bromine and iodine atoms.

Examples of the alkyl group of R⁵ include methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, tert-butyl, n-pentyl and n-hexyl groups. C₁ to C₄ alkyl groups are preferred, and methyl group and an ethyl group are more preferred.

Examples of the alkyl group having a halogen atom of R⁵ include trifluoromethyl, perfluoroethyl, perfluoropropyl, perfluoro-isopropyl, perfluorobutyl, perfluoro-sec-butyl, perfluoro-tert-butyl, perfluoropentyl, perfluorohexyl, trichloromethyl, tribromomethyl and triiodomethyl groups.

R⁵ is preferably a hydrogen atom or a C₁ to C₄ alkyl group, more preferably a hydrogen atom, a methyl group or an ethyl group, and still more preferably a hydrogen atom or a methyl group.

Examples of the alkanediyl group of A⁵ include methylene, ethylene, propane-1,3-diyl, propane-1,2-diyl, butane-1,4-diyl, pentane-1,5-diyl, hexane-1,6-diyl, butane-1,3-diyl, 2-methylpropane-1,3-diyl, 2-methylpropane-1,2-diyl, pentane-1,4-diyl and 2-methylbutane-1,4-diyl groups.

Examples of a group in which a methylene group contained in the alkanediyl group of A⁵ has been replaced by the oxygen atom or a carbonyl group include *-A²-O—, *-A²-CO—O—, *-A²-CO—O-A³-CO—O— and *-A²-O—CO-A³-O—.

A² and A³ each independently represent a C₁ to C₆ alkanediyl group.

Examples of the alkanediyl group of A² and A³ include the same as those of the alkanediyl group of A⁵.

A⁴ is preferably an oxygen atom.

A⁵ is preferably a single bond or *-A²-CO—O—, and more preferably *—CH₂—CO—O— or *—C₂H₄—CO—O—.

Examples of structures represented by the formula (a3-4I ) include the following ones. In each of the formulae, t represents an integer of 1 to 6.

The structural unit having an adamantane lactone group is preferably a structural unit represented by formula (a3-4I):

wherein R⁵ represents a hydrogen atom, a halogen atom, or a C₁ to C₆ alkyl group that may have a fluorine atom,

A⁴ represents an oxygen atom or an NH group, and

A⁵ represents a single bond or a C₁ to C₈ alkanediyl group where a methylene group may be replaced by an oxygen atom or a carbonyl group.

The structural unit having an adamantane lactone group is more preferably a structural unit represented by formula (a3-4′):

wherein R⁵ represents a hydrogen atom, a halogen atom, or a C₁ to C₆ alkyl group that may have a fluorine atom,

A¹ represents a single bond, *-A²-O—, *-A²-CO—O—, *-A²-CO—O-A³-CO—O— or *-A²-O—CO-A³-O— where * represents a binding site to an oxygen atom, and A² and A³ each independently represent a C₁ to C₆ alkanediyl group.

Examples of the alkanediyl group of A² and A³ include methylene, ethylene, propane-1,3-diyl, propane-1,2-diyl, butane-1,4-diyl, pentane-1,5-diyl, hexane-1,6-diyl, butane-1,3-diyl, 2-methylpropane-1,3-diyl, 2-methylpropane-1,2-diyl, pentane-1,4-diyl and 2-methylbutane-1,4-diyl groups.

A¹ is preferably a single bond or *-A²-CO—O—, and more preferably a single bond, —CH₂—CO—O— or —C₂H₄—CO—O—.

Examples of the structural unit having an adamantane lactone group include the following ones.

Examples of the structural unit having an adamantane lactone group include those in which a methyl group corresponding to R⁵ in the structural units represented by the above formulae has been replaced by a hydrogen atom.

The structural unit having adamantane lactone has preferably an adamantane lactone represented by formula (a3-4II-a) or formula (a3-4II-b) usually at the side chain end of it. In each of the formulae, * represents a binding site to A¹:

Specific examples of the structural unit having an adamantane lactone group preferably include the following ones.

Examples of the structural unit having an adamantane lactone group include those in which a methyl group corresponding to R⁵ in the structural units represented by the above formulae has been replaced by a hydrogen atom.

The structural unit represented by formula (a3-4′) is derived from a compound represented by formula (a3-4″) (which is sometimes referred to as “compound (a3-4″)”):

wherein R⁵ and A¹ are as defined above.

The compound (a3-4″) can be produced according to the method described in JP2014-16600A, and is available on the market.

The proportion of the structural unit (a4) is preferably 20 to 97% by mole, preferably 25 to 95% by mole, more preferably 30 to 90% by mole, with respect to the total structural units (100% by mole) of the resin (A1).

The structural unit having an adamantane lactone group is generally 3 to 80% by mole, preferably 5 to 75% by mole, more preferably 5 to 70% by mole, further more preferably 5 to 50% by mole, still further more preferably 5 to 20% by mole, with respect to the total structural units (100% by mole) of the resin (A1).

When the proportions of the structural unit (a4) and the structural unit having an adamantane lactone group are within the above ranges, resist patterns with reduced LER and reduced defects can be produced.

The resin (A1) can be produced by a known polymerization method, for example, radical polymerization method, using one or more species of monomers inducing the structural units as described above, such as the monomer (a4′-0), the monomer (a4′-1), the monomer (a4′-2), the monomer (a4′-3) and the monomer (a3-4″), and optionally one or more of a monomer represented by formula (I′) and/or other monomers having no acid-labile group, as described below. The proportion of the structural unit in the resin (A1) can be adjusted by changing the amount of a monomer used in polymerization.

The resin (A1) preferably further include a structural unit represented by formula (I) which is different from the structural unit (a2) and the structural unit (a3) described below (which is sometimes referred to as “structural unit (I)”).

In the formula, R¹ represents a hydrogen atom or a methyl group,

L¹ represents a single bond or a C₁ to C₁₈ divalent saturated hydrocarbon group where a methylene group may be replaced by an oxygen atom or a carbonyl group, and

R² represents a C₃ to C₁₈ alicyclic hydrocarbon group where a hydrogen atom may be replaced by a C₁ to C₈ aliphatic hydrocarbon group or a hydroxy group, provided that the carbon atom directly bonded to L¹ has no aliphatic hydrocarbon group by which a hydrogen atom has been replaced.

A methylene group contained in the saturated hydrocarbon group of L¹ may be replaced by an oxygen atom, and an ethylene group contained in the saturated hydrocarbon group of L¹ may be replaced by an ester group.

Examples of the alicyclic hydrocarbon group of R² include any one of a monocyclic group or a polycyclic group. Examples of the monocyclic alicyclic hydrocarbon group include cyclopropyl, cyclobutyl, cyclopentyl and cyclohexyl groups. Examples of the polycyclic hydrocarbon group include adamantyl and norbornyl groups.

Examples of the C₁ to C₈ aliphatic hydrocarbon group include an alkyl group such as methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, tert-butyl, n-pentyl, n-hexyl, n-heptyl, 2-ethylhexyl and n-octyl groups.

Examples of the alicyclic hydrocarbon group having a substituent of R² include 3-hydroxyadamantyl group and 3-methyladamantyl group.

R² is preferably an unsubstituted C₃ to C₁₈ alicyclic hydrocarbon group, and more preferably an adamantyl, norbornyl or cyclohexyl group.

Examples of the divalent saturated hydrocarbon group of L¹ include a saturated aliphatic hydrocarbon group and a saturated alicyclic hydrocarbon group, and a saturated aliphatic hydrocarbon group is preferred.

Examples of the saturated aliphatic hydrocarbon group include an alkanediyl such as methylene, ethylene, propanediyl, butanediyl and pentanediyl.

Examples of the saturated alicyclic hydrocarbon group include any of a monocyclic group and a polycyclic group. Examples of the monocyclic group include cycloalkanediyl group such as cyclopentanediyl and cyclohexanediyl groups. Examples of the polycyclic group include adamantanediyl and norbornanediyl groups.

Examples of the saturated hydrocarbon group in which a methylene group has been replaced by an oxygen atom or a carbonyl group include groups represented by the formula (L1-1) to the formula (L1-4). In the formula (L1-1) to the formula (L1-4), * represents a binding site to an oxygen atom.

In the formulae, X^(X1) represents an oxycarbonyl group or a carbonyloxy group,

L^(X1) represents a C₁ to C₁₆ divalent saturated aliphatic hydrocarbon group,

L^(X2) represents a single bond or a C₁ to C₁₅ divalent saturated aliphatic hydrocarbon group,

provided that the total carbon number contained in the groups of L^(X1) and L^(X2) is 16 or less;

L^(X3) represents a single bond or a C₁ to C₁₇ divalent saturated aliphatic hydrocarbon group,

L^(X4) represents a single bond or a C₁ to C₁₆ divalent saturated aliphatic hydrocarbon group,

provided that the total carbon number contained in the groups of L^(X3) and L^(X4) is 17 or less;

L^(X5) represents a C₁ to C₁₅ divalent saturated aliphatic hydrocarbon group,

L^(X6) and L^(X7) each independently represent a single bond or a C₁ to C₁₄ divalent saturated aliphatic hydrocarbon group,

provided that the total carbon number contained in the groups of L^(X5), L^(X6) and L^(X7) is 15 or less;

L^(X8) and L^(X9) each independently represent a single bond or a C₁ to C₁₂ divalent saturated aliphatic hydrocarbon group,

W^(X1) represents a C₃ to C₁₅ divalent saturated alicyclic hydrocarbon group, provided that the total carbon number contained in the groups of L^(X8), L^(X9) and W^(X1) is 15 or less.

L^(X1) is preferably a C₁ to C₈ divalent saturated aliphatic hydrocarbon group, and more preferably a methylene or ethylene group.

L^(X2) is preferably a single bond or a C₁ to C₈ divalent saturated aliphatic hydrocarbon group, and more preferably a single bond.

L^(X3) is preferably a C₁ to C₈ divalent saturated aliphatic hydrocarbon group.

L^(X4) is preferably a single bond or a C₁ to C₈ divalent saturated aliphatic hydrocarbon group.

L^(X5) is preferably a C₁ to C₈ divalent saturated aliphatic hydrocarbon group, and more preferably methylene or ethylene group.

L^(X6) is preferably a single bond or a C₁ to C₈ divalent saturated aliphatic hydrocarbon group, and more preferably methylene or ethylene group.

L^(X7) is preferably a single bond or a C₁ to C₈ divalent saturated aliphatic hydrocarbon group.

L^(X8) is preferably a single bond or a C₁ to C₈ divalent saturated aliphatic hydrocarbon group, and more preferably a single bond or a methylene group.

L^(X9) is preferably a single bond or a C₁ to C₈ divalent saturated aliphatic hydrocarbon group, and more preferably a single bond or methylene group.

W^(X1) is preferably a C₃ to C₁₀ divalent saturated alicyclic hydrocarbon group, and more preferably a cyclohexanediyl or adamantanediyl group.

Examples of the group represented by the formula (L1-1) include the following ones.

Examples of the group represented by the formula (L1-2) include the following ones.

Examples of the group represented by the formula (L1-3) include the following ones.

Examples of the group represented by the formula (L1-4) include the following ones.

L¹ is preferably a single bond or the groups represented by the formula (L1-1).

Examples of the structural unit (I) include the following ones.

Examples of the structural unit (I) include those in which a methyl group corresponding to R¹ has been replaced by a hydrogen atom in the structural units represented by the above formulae.

The structural unit (I) is derived from a compound represented by formula (I′) (which is sometimes referred to as “compound (I′)”):

wherein R¹, L¹ and R² are as defined above.

As the compound (I′), a marketed product or a compound which is produced by a known method may be used.

The known method includes a method in which (meth)acrylic acid or derivatives thereof, for example, (meth)acrylic chloride is condensed with a suitable alcohol (HO-L¹-R²). Examples of the marketed product include adamantane-1-yl methacrylate and adamantane-1-yl acrylate.

When the resin (A1) includes the structural unit (I), the proportion of the structural unit (a4) is preferably 20 to 80% by mole, more preferably 25 to 70% by mole, still more preferably 30 to 60% by mole, with respect to the total structural units (100% by mole) of the resin (A1).

When the resin (A1) includes the structural unit (I), the proportion of the structural unit having an adamantane lactone group is preferably 3 to 50% by mole, more preferably 5 to 40% by mole, still more preferably 3 to 30% by mole, with respect to the total structural units (100% by mole) of the resin (A1).

When the resin (A1) includes the structural unit (I), the proportion of the structural unit (I) is preferably 17 to 77% by mole, more preferably 25 to 70% by mole, still more preferably 35 to 65% by mole, with respect to the total structural units (100% by mole) of the resin (A1).

When the proportions of the structural unit (a4), the structural unit having an adamantane lactone group ant the structural unit (I) are within the above ranges, resist patterns with excellent LER and reduced defects can be produced.

The resin (A1) may further include a structural unit (a3) which is other than the structural unit (a3-4I), and a structural unit (a2) and described below.

The weight average molecular weight of the resin (A1) is preferably 5,000 or more (more preferably 7,000 or more, and still more preferably 10,000 or more), and 80,000 or less (more preferably 50,000 or less, and still more preferably 30,000 or less).

In the present specification, the weight average molecular weight is a value determined by gel permeation chromatography using polystyrene as the standard product. The detailed condition of this analysis is described in Examples.

<Resin (A2)>

The resin (A2) includes a structural unit having an acid-labile group (which is sometimes referred to as “structural unit (a1)”). Also, the resin (A2) may preferably include a structural unit other than the structural unit (a1). Examples of the structural unit other than the structural unit (a1) include a structural unit having no acid-labile group (which is sometimes referred to as “structural unit (s)”), a structural unit other than the structural unit (a1), a structural unit (a2) as described later and a structural unit (a3) as described later (which is sometimes referred to as “structural unit (t)”).

<Structural Unit (a1)>

The structural unit (a1) is derived from a monomer having an acid-labile group (which is sometimes referred to as “monomer (a1)”).

In the resin (A2), the acid-labile group contained in the structural unit (a1) is preferably the following group (1) and/or group (2):

wherein R^(a1) to R^(a3) each independently represent a C₁ to C₈ alkyl group, a C₃ to C₂₀ alicyclic hydrocarbon group or combination thereof, or R^(a1) and R^(a2) may be bonded together with a carbon atom bonded thereto to form a C₃ to C₂₀ divalent alicyclic hydrocarbon group;

na represents an integer of 0 or 1; and

* represents a binding site;

wherein R^(a1′) and R^(a2′) each independently represent a hydrogen atom or a C₁ to C₁₂ hydrocarbon group, R^(a3′) represents a C₁ to C₂₀ hydrocarbon group, or R^(a2′) and R^(a3′) may be bonded together with a carbon atom and X bonded thereto to form a divalent C₃ to C₂₀ heterocyclic group, and a methylene group contained in the hydrocarbon group or the divalent heterocyclic group may be replaced by an oxygen atom or a sulfur atom;

X represents —O— or —S—; and

* represents a binding site.

Examples of the alkyl group of R^(a1) to R^(a3) include methyl, ethyl, propyl, n-butyl, n-pentyl, n-hexyl, n-heptyl and n-octyl groups.

Examples of the alicyclic hydrocarbon group of R^(a1) to R^(a3) include monocyclic groups such as a cycloalkyl group, i.e., cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl groups; and polycyclic groups such as decahydronaphtyl, adamantyl and norbornyl groups as well as the following groups. In each of the formulae, * represents a binding site.

The carbon number of the alicyclic hydrocarbon group of R^(a1) to R^(a3) is preferably 3 to 16.

Examples of groups combining the alkyl group and the alicyclic hydrocarbon group include methyl cyclohexyl, dimethyl cyclohexyl, methyl norbornyl and cyclohexylmethl, adamantylmethyl and norbornyletyl groups.

na is preferably 0.

When R^(a1) and R^(a2) is bonded together to form a divalent alicyclic hydrocarbon group, examples of the group-C(R^(a1))(R^(a2))(R^(a3)) include the following groups. The carbon number of the divalent alicyclic hydrocarbon group is preferably 3 to 12. In each of the formulae, * represent a binding site to —O—.

In each formula, R^(a3) is as defined above.

Specific examples of the group represented by the formula (1) include, for example,

1,1-dialkylalkoxycarbonyl group (a group in which R^(a1) to R^(a3) are alkyl groups, preferably tert-butoxycarbonyl group, in the formula (1)),

2-alkyladamantane-2-yloxycarbonyl group (a group in which R^(a1), R^(a2) and a carbon atom form adamantyl group, and R^(a3) is alkyl group, in the formula (1)), and

1-(adamantane-1-yl)-1-alkylalkoxycarbonyl group (a group in which R^(a1) and R^(a2) are alkyl group, and R^(a3) is adamantyl group, in the formula (1)).

The hydrocarbon group of R^(a1′) to R^(a3′) includes any of an alkyl group, an alicyclic hydrocarbon group, an aromatic hydrocarbon group and a group formed by combining thereof.

Examples of the alkyl group and the alicyclic hydrocarbon group are the same examples as described above.

Examples of the aromatic hydrocarbon group include an aryl group such as phenyl, naphthyl, anthryl, p-methylphenyl, p-tert-butylphenyl, p-adamantylphenyl, tolyl, xylyl, cumenyl, mesityl, biphenyl, phenanthryl, 2,6-diethylphenyl and 2-methyl-6-ethylphenyl groups.

Examples of the divalent heterocyclic group formed by bonding with R^(a2′) and R^(a3′) include the following groups.

In each formula, R^(a1′) and X are as defined above.

At least one of R^(a1′) and R^(a2′) is preferably a hydrogen atom.

Specific examples of the group represented by the formula (2) include the following groups. In each of the formulae, * represents a binding site.

The monomer (a1) is preferably a monomer having an acid-labile group and an ethylenically unsaturated bond, and more preferably a (meth)acrylic monomer having an acid-labile group.

Among the (meth)acrylic monomer having an acid-labile group, a monomer having a C₅ to C₂₀ alicyclic hydrocarbon group is preferred. When a resin (A2) having a structural unit derived from a monomer (a1) having a bulky structure such as the alicyclic hydrocarbon group is used for a resist composition, the resist composition having excellent resolution tends to be obtained.

Examples of a structural unit derived from the (meth)acrylic monomer having the group represented by the formula (1) preferably include structural units represented by the formula (a1-0), the formula (a1-1) and the formula (a1-2) below. These may be used as a single structural unit or as a combination of two or more structural units. The structural unit represented by the formula (a1-0), the structural unit represented by the formula (a1-1) and a structural unit represented by the formula (a1-2) are sometimes referred to as “structural unit (a1-0)”, “structural unit (a1-1)” and “structural unit (a1-2)”), respectively, and monomers inducing the structural unit (a1-0), the structural unit (a1-1) and the structural unit (a1-2) are sometimes referred to as “monomer (a1-0)”, “monomer (a1-1)” and “monomer (a1-2)”), respectively:

wherein L^(a01) represents —O— or *—O—(CH₂)_(k01)—CO—O—,

k01 represents an integer of 1 to 7,

* represents a binding site to —CO—,

R^(a01) represents a hydrogen atom or a methyl group, and

R^(a02), R^(a03) and R^(a04) each independently represent a C₁ to C₈ alkyl group, a C₃ to C₁₈ alicyclic hydrocarbon group or a combination thereof.

L^(a01) is preferably an —O— or *—O—(CH₂)_(k01)—CO—O— in which k01 is preferably an integer of 1 to 4, more preferably an integer of 1, more preferably an —O—.

Examples of the alkyl group and an alicyclic hydrocarbon group of R^(a02), R^(a03) and R^(a04) and the combination thereof are the same examples as the group described in R^(a1) to R^(a3) in the formula (1).

The alkyl group of R^(a02), R^(a03) and R^(a04) is preferably a C₁ to C₆ alkyl group.

The alicyclic hydrocarbon group of R^(a02), R^(a03) and R^(a04) is preferably a C₃ to C₈ alicyclic hydrocarbon group, more preferably a C₃ to C₆ alicyclic hydrocarbon group.

The group formed by combining the alkyl group and the alicyclic hydrocarbon group has preferably 18 or less of carbon atom. Examples of those groups include methylcyclohexyl, dimethylcyclohexyl and methylnorbornyl groups.

R^(a02) and R^(a03) is preferably a C₁ to C₆ alkyl group, more preferably a methyl or ethyl group.

R^(a04) is preferably a C₁ to C₆ alkyl group or a C₅ to C₁₂ alicyclic hydrocarbon group, more preferably methyl, ethyl, cyclohexyl or adamantyl group.

In each formula, L^(a1) and L^(a2) each independently represent —O— or *—O—(CH₂)_(k1)—CO—O—,

k1 represents an integer of 1 to 7,

* represents a binding site to —CO—,

R^(a4) and R^(a5) each independently represent a hydrogen atom or a methyl group,

R^(a6) and R^(a7) each independently represent a C₁ to C₈ alkyl group, a C₃ to C₁₈ alicyclic hydrocarbon group or a combination thereof,

m1 represents an integer of 0 to 14,

n1 represents an integer of 0 to 10, and

n1′ represents an integer of 0 to 3.

L^(a1) and L^(a2) are preferably —O— or *—O—(CH₂)_(k1′)—CO—O— in which k1′ represents an integer of 1 to 4 and more preferably 1, and still more preferably —O—.

R^(a4) and R^(a5) are preferably a methyl group.

Examples of the alkyl group of R^(a6) and R^(a7) include methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, tert-butyl, n-pentyl, n-hexyl, n-heptyl, 2-ethylhexyl and n-octyl groups.

Examples of the alicyclic hydrocarbon group of R^(a6) and R^(a7) include monocyclic hydrocarbon groups such as a cycloalkyl group, i.e., cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, methylcyclohexyl, dimethylcyclohexyl, cycloheptyl, cyclooctyl and cyclodecyl groups; and polycyclic hydrocarbon groups such as decahydronaphtyl, adamantyl, 2-alkyadamantane-2-yl, 1-(adamantane-1-yl)alkane-1-yl, norbornyl, methyl norbornyl and isobornyl groups.

Examples of group formed by combining the alkyl group and the alicyclic hydrocarbon group of R^(a6) and R^(a7) include an aralkyl group such as benzyl and phenethyl groups.

The alkyl group of R^(a6) and R^(a7) is preferably a C₁ to C₆ alkyl group.

The alicyclic hydrocarbon group of R^(a6) and R^(a7) is preferably a C₃ to C₈ alicyclic hydrocarbon group, and more preferably a C₃ to C₆ alicyclic hydrocarbon group.

m1 is preferably an integer of 0 to 3, and more preferably 0 or 1.

n1 is preferably an integer of 0 to 3, and more preferably 0 or 1.

n1′ is preferably 0 or 1, and more preferably 1.

Examples of the monomer (a1-0) preferably include monomers represented by formula (a1-0-1) to formula (a1-0-12), and more preferably monomers represented by formula (a1-0-1) to formula (a1-0-10) below.

Examples of the structural units (a1-0) include structural units in which a methyl group corresponding to R^(a01) has been replaced by a hydrogen atom in the structural units represented by the above formulae.

Examples of the monomer (a1-1) include monomers described in JP 2010-204646A. Among these, the monomers are preferably monomers represented by formula (a1-1-1) to formula (a1-1-8), and more preferably monomers represented by formula (a1-1-1) to formula (a1-1-4) below.

Examples of the monomer (a1-2) include 1-methylcyclopentane-1-yl (meth)acrylate, 1-ethylcyclopentane-1-yl (meth)acrylate, 1-methylcyclohexane-1-yl (meth)acrylate, 1-ethylcyclohexane-1-yl (meth)acrylate, 1-ethylcycloheptane-1-yl (meth)acrylate, 1-ethylcyclooctane-1-yl (meth)acrylate, 1-isopropylcyclopentane-1-yl (meth)acrylate and 1-isopropylcyclohexane-1-yl (meth)acrylate. Among these, the monomers are preferably monomers represented by formula (a1-2-1) to formula (a1-2-12), and more preferably monomers represented by formula (a1-2-3), formula (a1-2-4), formula (a1-2-9) and formula (a1-2-10), and still more preferably monomer represented by formula (a1-2-3) and formula (a1-2-9) below.

When the resin (A2) includes the structural unit (a1-0) and/or the structural unit (a1-1) and/or the structural unit (a1-2), the total proportion thereof is generally 10 to 95% by mole, preferably 15 to 90% by mole, and more preferably 20 to 85% by mole, with respect to the total structural units (100% by mole) of the resin (A2).

Further, examples of the structural unit (a1) having the group (1) include a structural unit presented by formula (a1-3). The structural unit represented by the formula (a1-3) is sometimes referred to as “structural unit (a1-3)”. The monomer from which the structural unit (a1-3) is derived is sometimes referred to as “monomer (a1-3)”.

In the formula, R^(a9) represents a carboxy group, a cyano group, a —COOR^(a13), a hydrogen atom or a C₁ to C₃ aliphatic hydrocarbon group that may have a hydroxy group,

R^(a13) represents a C₁ to C₈ aliphatic hydrocarbon group, a C₃ to C₂₀ alicyclic hydrocarbon group or a group formed by combining thereof, a hydrogen atom contained in the aliphatic hydrocarbon group and the alicyclic hydrocarbon group may be replaced by a hydroxy group, a methylene group contained in the aliphatic hydrocarbon group and the alicyclic hydrocarbon group may be replaced by an oxygen atom or a carbonyl group, and

R^(a10), R^(a11) and R^(a12) each independently represent a C₁ to C₈ alkyl group, a C₃ to C₂₀ alicyclic hydrocarbon group or a group formed by combining thereof, or R^(a10) and R^(a11) may be bonded together with a carbon atom bonded thereto to form a C₁ to C₂₀ divalent hydrocarbon group.

Here, examples of —COOR^(a13) group include a group in which a carbonyl group is bonded to the alkoxy group, such as methoxycarbonyl and ethoxycarbonyl groups.

Examples of the aliphatic hydrocarbon group that may have a hydroxy group of R^(a9) include methyl, ethyl, propyl, hydroxymethyl and 2-hydroxyethyl groups.

Examples of the C₁ to C₈ aliphatic hydrocarbon group of R^(a13) include methyl, ethyl, propyl, isopropyl, n-butyl, sec-butyl, tert-butyl, n-pentyl, n-hexyl, n-heptyl, 2-ethylhexyl and n-octyl groups.

Examples of the C₃ to C₂₀ alicyclic hydrocarbon group of R^(a13) include cyclopentyl, cyclopropyl, adamantyl, adamantylmetyl, 1-(adamantyl-1-yl)-methylethyl, 2-oxo-oxolane-3-yl, 2-oxo-oxolane-4-yl groups.

Examples of the alkyl group of R^(a10) to R^(a12) include methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, tert-butyl, n-pentyl, n-hexyl, n-heptyl, 2-ethylhexyl and n-octyl groups.

Examples of the alicyclic hydrocarbon group of R^(a10) and R^(a12) include monocyclic groups such as a cycloalkyl group, i.e., cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, methylcyclohexyl, dimethylcyclohexyl, cycloheptyl, cyclooctyl and cyclodecyl groups; and polycyclic groups such as decahydronaphtyl, adamantyl, 2-alkyl-2-adamantyl, 1-(adamantane-1-yl)alkane-1-yl, norbornyl, methyl norbornyl and isobornyl groups.

When R^(a10) and R^(a11) are bonded together with a carbon atom bonded thereto to form a divalent hydrocarbon group, examples of the group-C(R^(a10))(R^(a11))(R^(a12)) include the following groups.

In each formula, R^(a12) is as defined above.

Examples of the monomer (a1-3) include tert-butyl 5-norbornene-2-carboxylate, 1-cyclohexyl-1-methylethyl 5-norbornene-2-carboxylate, 1-methylcyclohexyl 5-norbornene-2-carboxylate, 2-methy-2-adamantane-2-yl 5-norbornene-2-carboxylate, 2-ethyl-2-adamantane-2-yl 5-norbornene-2-carboxylate, 1-(4-methycyclohexyl)-1-methylethyl 5-norbornene-2-carboxylate, 1-(4-hydroxycyclohexyl)-1-methylethyl 5-norbornene-2-carboxylate, 1-methyl-(4-oxocyclohexyl)-1-ethyl 5-norbornene-2-carboxylate, and 1-(1-adamantane-1-yl)-1-methylethyl 5-norbornene-2-carboxylate.

The resin (A2) having the structural unit (a1-3) can improve the resolution of the obtained resist composition because it has a bulky structure, and also can improve a dry-etching tolerance of the obtained resist composition because of incorporated a rigid norbornene ring into a main chain of the resin (A2).

When the resin (A2) includes the structural unit (a1-3), the proportion thereof is preferably 10% by mole to 95% by mole, more preferably 15% by mole to 90% by mole, and still more preferably 20% by mole to 85% by mole, with respect to the total structural units constituting the resin (A2) (100% by mole).

Examples of a structural unit (a1) having the group (2) include a structural unit represented by formula (a1-4). The structural unit is sometimes referred to as “structural unit (a1-4)”.

In the formula, R^(a32) represents a hydrogen atom, a halogen atom or a C₁ to C₆ alkyl group that may have a halogen atom,

R^(a33) in each occurrence independently represent a halogen atom, a hydroxy group, a C₁ to C₆ alkyl group, a C₁ to C₆ alkoxy group, a C₂ to C₄ acyl group, a C₂ to C₄ acyloxy group, an acryloyloxy group or methacryloyloxy group,

1a represents an integer 0 to 4,

R^(a34) and R^(a35) each independently represent a hydrogen atom or a C₁ to C₁₂ hydrocarbon group; and

R^(a36) represents a C₁ to C₂₀ hydrocarbon group, or R^(a35) and R^(a36) may be bonded together with a C—O bonded thereto to form a divalent C₂ to C₂₀ hydrocarbon group, and a methylene group contained in the hydrocarbon group or the divalent hydrocarbon group may be replaced by an oxygen atom or a sulfur atom.

Examples of the alkyl group of R^(a32) and R^(a33) include methyl, ethyl, propyl, isopropyl, butyl, pentyl and hexyl groups. The alkyl group is preferably a C₁ to C₄ alkyl group, and more preferably a methyl or ethyl group, and still more preferably a methyl group.

Examples of the halogen atom of R^(a32) and R^(a33) include a fluorine, chlorine, bromine and iodine atoms.

Examples of the alkyl group that may have a halogen atom include trifluoromethyl, difluoromethyl, methyl, perfluoromethyl, 1,1,1-trifluoroethyl, 1,1,2,2-tetrafluoroethyl, ethyl, perfluoropropyl, 1,1,1,2,2-pentafluoropropyl, propyl, perfluorobutyl, 1,1,2,2,3,3,4,4-octafluorobutyl, butyl, perfluoropentyl, 1,1,1,2,2,3,3,4,4-nonafluoropentyl, n-pentyl, n-hexyl and n-perfluorohexyl groups.

Examples of an alkoxy group include methoxy, ethoxy, propoxy, butoxy, pentyloxy and hexyloxy groups. The alkoxy group is preferably a C₁ to C₄ alkoxy group, more preferably a methoxy group and an ethoxy group, and still more preferably a methoxy group.

Examples of the acyl group include acetyl, propanonyl and butylyl groups.

Examples of the acyloxy group include acetyloxy, propanonyloxy and butylyloxy groups.

Examples of the hydrocarbon group of R^(a34) and R^(a35) are the same examples as described in R^(a1′) to R^(a2′) in the formula (2).

Examples of hydrocarbon group of R^(a36) include a C₁ to C₁₈ alkyl group, a C₃ to C₁₈ alicyclic hydrocarbon group, a C₆ to C₁₈ aromatic hydrocarbon group or a group formed by combining thereof.

In the formula (a1-4), R^(a32) is preferably a hydrogen atom.

R^(a33) is preferably a C₁ to C₄ alkoxy group, more preferably a methoxy group and an ethoxy group, and still more preferably a methoxy group.

1a is preferably 0 or 1, and more preferably 0.

R^(a34) is preferably a hydrogen atom.

R^(a35) is preferably a C₁ to C₁₂ hydrocarbon group, and more preferably a methyl or an ethyl group.

The hydrocarbon group of R^(a36) is preferably a C₁ to C₁₈ alkyl group, a C₃ to C₁₈ alicyclic hydrocarbon group, a C₆ to C₁₈ aromatic hydrocarbon group or a combination thereof, and more preferably a C₁ to C₁₈ alkyl group, a C₃ to C₁₈ alicyclic hydrocarbon group or a C₇ to C₁₈ aralkyl group. The alkyl group and the alicyclic hydrocarbon group of R^(a36) are preferably unsubstituted. When the aromatic hydrocarbon group of R^(a36) has a substituent, the substituent is preferably a C₆ to C₁₀ aryloxy group.

Examples of the monomer from which the structural unit (a1-4) is derived include monomers described in JP 2010-204646A. Among these, the monomers are preferably the following monomers represented by the formula (a1-4-1) to the formula (a1-4-7), and more preferably monomers represented by the formula (a1-4-1) to the formula (a1-4-5).

When the resin (A2) includes the structural unit (a1-4), the proportion thereof is preferably 10% by mole to 95% by mole, more preferably 15% by mole to 90% by mole, and still more preferably 20% by mole to 85% by mole, with respect to the total structural units constituting the resin (A2) (100% by mole).

Examples of the structural unit having an acid-labile group include a structural unit represented by formula (a1-5). The structural unit is sometimes referred to as “structural unit (a1-5)”.

In the formula (a1-5), R^(a8) represents a hydrogen atom, a halogen atom or a C₁ to C₆ alkyl group that may have a halogen atom,

Z^(a1) represent a single bond or *—(CH₂)_(h3)—CO-L⁵⁴-,

h3 represents an integer of 1 to 4,

* represents a binding site to L⁵¹,

L⁵¹, L⁵² and L⁵³ each independently represent —O— or —S—,

s1 represents an integer of 1 to 3, and

s1′ represents an integer of 0 to 3.

In the formula (a1-5), R^(a8) is preferably a hydrogen atom, a methyl group or trifluoromethyl group;

L⁵¹ is preferably —O—;

L⁵² and L⁵³ are independently preferably —O— or —S—, and more preferably one is —O— and another is —S—.

s1 is preferably 1;

s1′ is preferably an integer of 0 to 2;

Z^(a1) is preferably a single bond or *—CH₂—CO—O—.

Examples of a monomer from which the structural unit (a1-5) is derived include a monomer described in JP 2010-61117A. Among these, the monomers are preferably monomers represented by the formula (a1-5-1) to the formula (a1-5-4), and more preferably monomers represented by the formula (a1-5-1) to the formula (a1-5-2) below.

When the resin (A2) includes the structural unit (a1-5), the proportion thereof is preferably 1% by mole to 50% by mole, more preferably 3% by mole to 45% by mole, and more preferably 5% by mole to 40% by mole, with respect to the total structural units (100% by mole) constituting the resin (A2).

The resin (A2) includes, as the structural unit (a1), preferably at least one, more preferably two or more structural units selected from the structural unit (a1-0), the structural unit (a1-1), the structural unit (a1-2) and the structural unit (a1-5), still more preferably a combination of the structural unit (a1-1) and the structural unit (a1-2), a combination of the structural unit (a1-1) and the structural unit (a1-5), a combination of the structural unit (a1-1) and the structural unit (a1-0), a combination of the structural unit (a1-2) and the structural unit (a1-0), a combination of the structural unit (a1-5) and the structural unit (a1-0), a combination of the structural unit (a1-0), the structural unit (a1-1) and the structural unit (a1-2), a combination of the structural unit (a1-0), the structural unit (a1-1) and the structural unit (a1-5). In particular, the resin (A2) includes, as the structural unit (a1), preferably at least one of the structural unit (a1-1) and the structural unit (a1-2) and more preferably the structural unit (a1-1) and the structural unit (a1-2).

<Structural Unit (s)>

The structural unit (s) is derived from a monomer having no acid-labile group (which monomer is sometimes referred to as “monomer (s)”).

As the monomer (s) from which the structural unit (s) is derived, a known monomer having no acid-labile group can be used.

As the structural unit (s), a structural unit having a hydroxy group or a lactone ring but having no acid-labile group is preferred. When a resin including the structural unit derived from a structural unit having a hydroxy group but having no acid-labile group (such structural unit is sometimes referred to as “structural unit (a2)”) and/or a structural unit having a lactone ring but having no acid-labile group (such structural unit is sometimes referred to as “structural unit (a3)”) is used, the adhesiveness of resist to a substrate and resolution of resist pattern tend to be improved.

<Structural Unit (a2)>

The structural unit (a2) having a hydroxy group may be an alcoholic hydroxy group or a phenolic hydroxy group.

When KrF excimer laser lithography (248 nm), or high-energy irradiation such as electron beam or EUV (extreme ultraviolet) is used for the resist composition, using the structural unit having a phenolic hydroxy group as the structural unit (a2) is preferred.

When ArF excimer laser lithography (193 nm) is used, using the structural unit having an alcoholic hydroxy group as the structural unit (a2) is preferred, and using the structural unit represented by the formula (a2-1) is more preferred.

The structural unit (a2) may be used as a single structural unit or as a combination of two or more structural units.

Examples of the structural unit (a2) having a phenolic hydroxy group include a structural unit represented by the formula (a2-0) (which is sometimes referred to as “structural unit (a2-0)”).

wherein R^(a30) represents a hydrogen atom, a halogen atom or a C₁ to C₆ alkyl group that may have a halogen atom,

R^(a31) in each occurrence independently represents a halogen atom, a hydroxy group, a C₁ to C₆ alkyl group, a C₁ to C₆ alkoxy group, a C₂ to C₄ acyl group, a C₂ to C₄ acyloxy group, an acryloyloxy group or methacryloyloxy group, and

ma represents an integer 0 to 4.

Examples of the alkyl group include methyl, ethyl, propyl, isopropyl, butyl, n-pentyl and n-hexyl groups.

Examples of the halogen atom include a chlorine atom, a fluorine atom and bromine atom.

Examples of a C₁ to C₆ alkyl group that may have a halogen atom of R^(a30) include trifluoromethyl, difluoromethyl, methyl, perfluoromethyl, 1,1,1-trifluoroethyl, 1,1,2,2-tetrafluoroethyl, ethyl, perfluoropropyl, 1,1,1,2,2-pentafluoropropyl, propyl, perfluorobutyl, 1,1,2,2,3,3,4,4-octafluorobutyl, butyl, perfluoropentyl, 1,1,1,2,2,3,3,4,4-nonafluoropentyl, n-pentyl, n-hexyl and n-perfluorohexyl groups.

R^(a30) is preferably a hydrogen atom or a C₁ to C₄ alkyl group, and more preferably a hydrogen atom, methyl or ethyl group, and still more preferably a hydrogen atom or methyl group.

Examples of a C₁ to C₆ alkoxy group of R^(a31) include methoxy, ethoxy, propoxy, butoxy, pentyloxy, and hexyloxy groups. R^(a31) is preferably a C₁ to C₄ alkoxy group, more preferably a methoxy and ethoxy group, and still more preferably methoxy group.

Examples of the acyl group include acetyl, propanonyl and butylyl groups.

Examples of the acyloxy group include acetyloxy, propanonyloxy and butylyloxy groups.

ma is preferably 0, 1 or 2, more preferably 0 or 1, still more preferably 0.

The structural unit (a2-0) having a phenolic hydroxy group is preferably a structural unit represented below.

Among these, a structural unit represented by the formula (a2-0-1) and the formula (a2-0-2) are preferred.

Examples of a monomer from which the structural unit (a2-0) is derived include monomers described in JP2010-204634A.

The resin (A2) which includes the structural units (a2) having a phenolic hydroxy group can be produced, for example, by polymerizing a monomer where its phenolic hydroxy group has been protected with a suitable protecting group, followed by deprotection. The deprotection is carried in such a manner that an acid-labile group in the structural unit (a1) is significantly impaired. Examples of the protecting group for a phenolic hydroxy group include an acetyl group.

When the resin (A2) includes the structural unit (a2-0) having the phenolic hydroxy group, the proportion thereof is preferably 5% by mole to 95% by mole, more preferably 10% by mole to 80% by mole, and still more preferably 15% by mole to 80% by mole, with respect to the total structural units (100% by mole) constituting the resin (A).

Examples of the structural unit (a2) having an alcoholic hydroxy group include the structural unit represented by the formula (a2-1) (which is sometimes referred to as “structural unit (a2-1)”).

In the formula (a2-1), L^(a3) represents —O— or *—O—(CH₂)_(k2)—CO—O—,

k2 represents an integer of 1 to 7,

* represents a binding site to —CO—,

R^(a14) represents a hydrogen atom or a methyl group,

R^(a15) and R^(a16) each independently represent a hydrogen atom, a methyl group or a hydroxy group, and

o1 represents an integer of 0 to 10.

In the formula (a2-1), L^(a3) is preferably —O—, —O—(CH₂)_(f1)—CO—O—, here f1 represents an integer of 1 to 4, and more preferably —O—.

R^(a14) is preferably a methyl group.

R^(a15) is preferably a hydrogen atom.

R^(a16) is preferably a hydrogen atom or a hydroxy group.

o1 is preferably an integer of 0 to 3, and more preferably an integer of 0 or 1.

Examples of the monomer from which the structural unit (a2-1) is derived include monomers described in JP 2010-204646A. Among these, the structural units (a2-1) are preferably structural units represented by the formula (a2-1-1) to the formula (a2-1-6), more preferably structural units represented by the formula (a2-1-1) to the formula (a2-1-4), and still more preferably structural units represented by the formula (a2-1-1) and the formula (a2-1-3).

When the resin (A2) includes the structural unit (a2-1) having an alcoholic hydroxy group, the proportion thereof is generally 1% by mole to 45% by mole, preferably 1% by mole to 40% by mole, more preferably 1% by mole to 35% by mole, and still more preferably 2% by mole to 20% by mole, with respect to the total structural units (100% by mole) constituting the resin (A2).

<Structural unit (a3)>

The lactone ring included in the structural unit (a3) may be a monocyclic ring such as β-propiolactone, γ-butyrolactone, δ-valerolactone, or a condensed ring of monocyclic lactone ring with another ring. Examples of the lactone ring preferably include γ-butyrolactone, amadantane lactone, or bridged ring with α-butyrolactone.

Examples of the structural unit (a3) include structural units represented by any of formula (a3-1), formula (a3-2) and formula (a3-3). Further, the structural unit (a3) may be the structural unit (a3-4I) as described above. These structural units may be used as a single unit or as a combination of two or more units.

In each formula, L^(a4) represents *—O— or *—O—(CH₂)_(k3)—CO—O—, k3 represents an integer of 1 to 7, * represents a binding site to a carbonyl group,

R^(a18) represents a hydrogen atom or a methyl group,

R^(a21) in each occurrence represents a C₁ to C₄ aliphatic hydrocarbon group, and

p1 represents an integer of 0 to 5,

L^(a5) represents *—O— or *—O—(CH₂)_(k3)—CO—O—, k3 represents an integer of 1 to 7, * represents a binding site to a carbonyl group,

R^(a19) represents a hydrogen atom or a methyl group,

R^(a22) in each occurrence represents a carboxy group, a cyano group or a C₁ to C₄ aliphatic hydrocarbon group,

q1 represents an integer of 0 to 3,

L^(a6) represents *—O— or *—O—(CH₂)_(k3)—CO—O—, k3 represents an integer of 1 to 7, * represents a binding site to a carbonyl group,

R^(a20) represents a hydrogen atom or a methyl group,

R^(a23) in each occurrence represents a carboxy group, a cyano group or a C₁ to C₄ aliphatic hydrocarbon group, and

r1 represents an integer of 0 to 3,

Examples of the aliphatic hydrocarbon group of R^(a21), R^(a2) and R^(a23) include an alkyl group such as methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl and tert-butyl groups.

In the formulae (a3-1) to (a3-3), L^(a4) to L^(a6) is independently preferably —O—, *—O—(CH₂)_(k3′)—CO—O—, here k3′ represents an integer of 1 to 4, more preferably —O— or *—O—CH₂—CO—O—, and still more preferably *—O—.

R^(a18) to R^(a21) is preferably a methyl group.

R^(a22) and R^(a23) are independently preferably a carboxy group, a cyano group or a methyl group.

p1, q1 and r1 are independently preferably an integer of 0 to 2, and more preferably 0 or 1.

When the structural unit (a3) has an adamantane lactone, it is preferably the structural unit represented by the formula (a3-4′), and more preferably the structural unit represented by the formula (a3-4′) which has the adamantane lactone represented by formula (a3-4II-a) or formula (a3-4II-b).

Examples of the monomer from which the structural unit (a3) is derived include monomers described in JP 2010-204646A, monomers described in JP2000-122294A and monomers described in JP2012-41274A. The structural units are preferably structural units represented by the formula (a3-1-1) to the formula (a3-1-4), the formula (a3-2-1) to the formula (a3-2-4), the formula (a3-3-1) to the formula (a3-3-4), the formula (a3-4-1) to the formula (a3-4-6), more preferably structural units represented by the formula (a3-1-1) to the formula (a3-1-2), the formula (a3-2-3), the formula (a3-2-4), the formula (a3-4-1) and the formula (a3-4-2), and still more preferably structural units represented by the formula (a3-1-1), the formula (a3-2-3) below.

When the resin (A2) includes the structural units (a3), the total proportion thereof is preferably 5% by mole to 70% by mole, more preferably 10% by mole to 65% by mole, still more preferably 10% by mole to 60% by mole, with respect to the total structural units (100% by mole) constituting the resin (A2).

The proportion each of the formula (a3-1), the formula (a3-2), the formula (a3-3) and the formula (a3-4) is preferably 5% by mole to 60% by mole, more preferably 5% by mole to 50% by mole, still more preferably 10% by mole to 50% by mole, with respect to the total structural units (100% by mole) constituting the resin (A2).

<Other structural unit (t)>

The resin (A2) may further include a structural unit other than the structural unit (a1) and the structural unit (s) described above (which is sometimes referred to as “structural unit (t)”). Examples of the structural unit (t) include the structural unit (a4) and the structural unit (I), and another structural unit other than the structural unit (a2) and the structural unit (a3).

When the resin (A2) includes the structural unit (a4), the proportion thereof is preferably 1 to 20% by mole, more preferably 2 to 15% by mole, and still more preferably 3 to 10% by mole, with respect to the total structural units (100% by mole) of the resin (A2).

When the resin (A2) includes the structural unit (I), the proportion thereof is preferably 1 to 30% by mole, more preferably 2 to 20% by mole, and still more preferably 3 to 15% by mole, with respect to the total structural units (100% by mole) of the resin (A2).

The resin (A2) is preferably a resin having the structural unit (a1) and the structural unit (s), that is, a copolymer of the monomer (a1) and the monomer (s). In this copolymer, the structural unit (a1) is preferably at least one of the structural unit (a1-1), the structural unit (a1-2) (preferably the structural unit having a cyclohexyl group or a cyclopentyl group) and the structural unit (a1-5), and more preferably is the structural unit (a1-1) or the structural unit (a1-2) (preferably the structural unit having a cyclohexyl group or a cyclopentyl group).

The structural unit (s) is preferably at least one of the structural unit (a2) and the structural unit (a3). The structural unit (a2) is preferably the structural unit represented by the formula (a2-1). The structural unit (a3) is preferably the structural unit having at least one of a γ-butyrolactone ring, a bridged ring including a α-butyrolactone ring or an adamantane lactone ring, i.e., the structural units (a3-1-1) to (a3-1-4), the structural units (a3-2-1) to (a3-2-4) and the structural units (a3-4-1) to (a3-4-2).

The proportion of the structural unit derived from the monomer having an adamantyl group (in particular, the structural unit (a1-1)) in the resin (A2) is preferably 15% by mole or more with respect to the structural units (a1). As the mole ratio of the structural unit derived from the monomer having an adamantyl group increases within this range, the dry etching resistance of the resulting resist improves.

The resin (A2) can be produced by a known polymerization method, for example, radical polymerization method, using one or more species of monomers inducing the structural units as described above. The proportion of the structural unit in the resin (A2) can be adjusted by changing the amount of a monomer used in polymerization.

The weight average molecular weight of the resin (A2) is preferably 2,000 or more (more preferably 2,500 or more, and still more preferably 3,000 or more), and 50,000 or less (more preferably 30,000 or less, and still more preferably 15,000 or less).

The proportion of the resin (A1) is preferably 1 to 60 parts by mass, more preferably 1 to 50 parts by mass, and still more preferably 1 to 40 parts by mass, in particular preferably 2 to 30 parts by mass, with respect to the resin (A2) (100 parts by mass).

<Resin (X)>

The resist composition of the disclosure may include a resin (X) other than the resin (A1) and the resin (A2). Examples of the resin (X) include a resin consisting of the structural unit (s) such as the structural unit (a2), the structural unit (a3).

The weight average molecular weight of the resin (X) is preferably 6,000 or more (more preferably 7,000 or more), and 80,000 or less (more preferably 60,000 or less). The method of measuring of the weight average molecular weight of the resin (X) is the same as the resin (A1).

When the resist composition includes the resin (X), the proportion thereof is preferably 1 to 60 parts by mass, more preferably 1 to 50 parts by mass, and still more preferably 1 to 40 parts by mass, in particular preferably 2 to 30 parts by mass, with respect to the resin (A1) (100 parts by mass).

The total proportion of the resin (A1) and the resin (A2) is preferably 80% by mass to 99% by mass, more preferably 90% by mass to 99% by mass, with respect to the total amount of solid components of the resist composition.

When the resist composition includes the resin (X), the total proportion of the resin (A1), the resin (A2) and the resin (X) is preferably 80% by mass to 99% by mass, more preferably 90% by mass to 99% by mass, with respect to the total amount of solid components of the resist composition.

The proportion of the solid components in the resist composition and that of the resins in the solid components can be measured with a known analytical method such as liquid chromatography and gas chromatography.

<Acid generator (B)>

The acid generator (B) may be an ionic acid generator or a non-ionic acid generator. The acid generator (B) may be used any an ionic acid generator and a non-ionic acid generator. Examples of the nonionic compounds for the acid generator include organic halogenated compounds; sulfonate esters, e.g. 2-nitrobenzylester, aromatic sulfonates, oximesulfonate, N-sulfonyloxyimide, sulfonyloxyketone, and diazonaphtoquione 4-sulfonate; sulfones, e.g., disulfone, ketosulfone, and sulfonium diazomethane. The ionic compounds for the acid generator include onium salts having an onium cation, e.g., diazonium salts, phosphonium salts, sulfonium salts and iodonium salts. Examples of the anions of onium salt include a sulfonic acid anion, a sulfonylimide anion, sulfonylmethide anion.

As the acid generator, the compounds giving an acid by radiation can be used, which are mentioned in JP63-26653A1, JP55-164824A1, JP62-69263A1, JP63-146038A1, JP63-163452A1, JP62-153853A1, JP63-146029A1, U.S. Pat. No. 3,779,778B1, U.S. Pat. No. 3,849,137B1, DE3914407 and EP126,712A1. The acid generator for the photoresist composition can be produced by the method described in the above-mentioned documents.

The acid generator is preferably a fluorine-containing compound, more preferably a salt represented by formula (B1) (which is sometimes referred to as “acid generator (B1)”):

wherein Q¹ and Q² each respectively represent a fluorine atom or a C₁ to C₆ perfluoroalkyl group,

L^(b1) represents a C₁ to C₂₄ divalent saturated hydrocarbon group where a methylene group may be replaced by an oxygen atom or a carbonyl group and a hydrogen atom may be replaced by a hydroxyl group or fluorine atom, and

Y represents an optionally substituted C₃ to C₁₈ alicyclic hydrocarbon group where a methylene group may be replaced by an oxygen atom, a carbonyl group or a sulfonyl group, and

Z⁺ represents an organic cation.

Examples of the perfluoroalkyl group of Q¹ and Q² include trifluoromethyl, perfluoroethyl, perfluoropropyl, perfluoro-isopropyl, perfluorobutyl, perfluoro-sec-butyl, perfluoro-tert-butyl, perfluoropentyl and perfluorohexyl groups.

Q¹ and Q² independently are preferably trifluoromethyl or fluorine atom, and both of Q¹ and Q² are more preferably a fluorine atom.

Examples of the divalent saturated hydrocarbon group of L^(b1) include any of a chain or a branched alkanediyl group, a divalent mono- or a poly-alicyclic saturated hydrocarbon group, and a combination thereof.

Specific examples of the chain alkanediyl group include methylene, ethylene, propane-1,3-diyl, propane-1,2-diyl, butane-1,4-diyl, pentane-1,5-diyl, hexane-1,6-diyl, heptane-1,7-diyl, octane-1,8-diyl, nonane-1,9-diyl, decane-1,10-diyl, undecane-1,11-diyl, dodecane-1,12-diyl, tridecane-1,13-diyl, tetradecane-1,14-diyl, pentadecane-1,15-diyl, hexadecane-1,16-diyl, heptadecane-1,17-diyl groups.

Specific examples of the branched chain alkanediyl group include ethane-1,1-diyl, propane-1,1-diyl, propane-1,2-diyl, propane-2,2-diyl, pentane-1,4-diyl, pentane-2,4-diyl, 2-methylpropane-1,3-diyl, 2-methylpropane-1,2-diyl and 2-methylbutane-1,4-diyl groups.

Specific examples of the mono-alicyclic saturated hydrocarbon group include a cycloalkanediyl group such as cyclobutan-1,3-diyl, cyclopentan-1,3-diyl, cyclohexane-1,4-diyl and cyclooctan-1,5-diyl groups.

Specific examples of the poly-alicyclic saturated hydrocarbon group include norbornane-1,4-diyl, norbornane-2,5-diyl, adamantane-1,5-diyl and adamantane-2,6-diyl groups.

Examples of the saturated hydrocarbon group of L^(b1) in which a methylene group has been replaced by oxygen atom or a carbonyl group include the following groups represented by formula (b1-1) to formula (b1-3):

wherein L^(b2) represents a single bond or a C₁ to C₂₂ divalent saturated hydrocarbon group where a hydrogen atom may be replaced by a fluorine atom;

L^(b3) represents a single bond or a C₁ to C₂₂ divalent saturated hydrocarbon group where a hydrogen atom may be replaced by a fluorine atom or a hydroxy group, and a methylene group may be replaced by an oxygen atom or a carbonyl group;

provided that the total carbon number contained in the group of L^(b2) and L^(b3) is 22 or less;

L^(b4) represents a single bond or a C₁ to C₂₂ divalent saturated hydrocarbon group where a hydrogen atom may be replaced by a fluorine atom;

L^(b5) represents a single bond or a C₁ to C₂₂ divalent saturated hydrocarbon group where a hydrogen atom may be replaced by a fluorine atom or a hydroxy group, and a methylene group may be replaced by an oxygen atom or a carbonyl group;

provided that the total carbon number contained in the group of L^(b4) and L^(b5) is 22 or less;

L^(b6) represents a single bond or a C₁ to C₂₃ divalent saturated hydrocarbon group where a hydrogen atom may be replaced by a fluorine atom or a hydroxy group;

L^(b7) represents a single bond or a C₁ to C₂₃ divalent saturated hydrocarbon group where a hydrogen atom may be replaced by a fluorine atom or a hydroxy group, and a methylene group may be replaced by an oxygen atom or a carbonyl group;

provided that the total carbon number contained in the group of L^(b6) and L^(b7) is 23 or less, and

* represents a binding site to —Y.

In formula (b1-1) to formula (b1-3), when a methylene group has been replaced by an oxygen atom or a carbonyl group, the carbon number of the saturated hydrocarbon group corresponds to the number of the carbon atom before replacement.

Examples of the divalent saturated hydrocarbon group are the same examples as the divalent saturated hydrocarbon group of L^(b1).

L^(b2) is preferably a single bond.

L^(b3) is preferably a C₁ to C₄ divalent saturated hydrocarbon group.

L^(b4) is preferably a C₁ to C₈ divalent saturated hydrocarbon group where a hydrogen atom may be replaced by a fluorine atom.

L^(b5) is preferably a single bond or a C₁ to C₈ divalent saturated hydrocarbon group.

L^(b6) is preferably a single bond or a C₁ to C₄ divalent saturated hydrocarbon group where a hydrogen atom may be replaced by a fluorine atom.

L^(b7) is preferably a single bond or a C₁ to C₁₈ divalent saturated hydrocarbon group where a hydrogen atom may be replaced by a fluorine atom or a hydroxy group, and where a methylene group may be replaced by an oxygen atom or a carbonyl group.

Among these, the group represented by the formula (b1-1) or the formula (b1-3) is preferred.

Examples of the divalent group represented by the formula (b1-1) include the following groups represented by formula (b1-4) to formula (b1-8):

wherein L^(b8) represents a single bond or a C₁ to C₂₂ divalent saturated hydrocarbon group where a hydrogen atom may be replaced by a fluorine atom or a hydroxy group;

L^(b9) represents a C₁ to C₂₀ divalent saturated hydrocarbon group;

L^(b10) represents a single bond or a C₁ to C₁₉ divalent saturated hydrocarbon group where a hydrogen atom may be replaced by a fluorine atom or a hydroxy group;

provided that the total carbon number contained in the group of L^(b9) and L^(b10) is 20 or less;

L^(b11) represents a C₁ to C₂₁ divalent saturated hydrocarbon group;

L^(b12) represents a single bond or a C₁ to C₂₀ divalent saturated hydrocarbon group where a hydrogen atom may be replaced by a fluorine atom or a hydroxy group;

provided that the total carbon number contained in the group of L^(b11) and L^(b12) is 21 or less;

L^(b13) represents a C₁ to C₁₉ divalent saturated hydrocarbon group;

L^(b14) represents a single bond or a C₁ to C₁₈ divalent saturated hydrocarbon group;

L^(b15) represents a single bond or a C₁ to C₁₈ divalent saturated hydrocarbon group where a hydrogen atom may be replaced by a fluorine atom or a hydroxy group;

provided that the total carbon number contained in the group of L^(b13), L^(b14) and L^(b15) is 19 or less;

L^(b16) represents a C₁ to C₁₈ divalent saturated hydrocarbon group;

L^(b17) represents a C₁ to C₁₈ divalent saturated hydrocarbon group;

L^(b18) represents a single bond or a C₁ to C₁₇ divalent saturated hydrocarbon group where a hydrogen atom may be replaced by a fluorine atom or a hydroxy group;

provided that the total carbon number contained in the group of L^(b16), L^(b17) and L^(b18) is 19 or less.

L^(b8) is preferably a C₁ to C₄ divalent saturated hydrocarbon group.

L^(b9) is preferably a C₁ to C₈ divalent saturated hydrocarbon group.

L^(b10) is preferably a single bond or a C₁ to C₁₉ divalent saturated hydrocarbon group, and more preferably a single bond or a C₁ to C₈ divalent saturated hydrocarbon group.

L^(b11) is preferably a C₁ to C₈ divalent saturated hydrocarbon group.

L^(b12) is preferably a single bond or a C₁ to C₈ divalent saturated hydrocarbon group.

L^(b13) is preferably a C₁ to C₁₂ divalent saturated hydrocarbon group.

L^(b14) is preferably a single bond or a C₁ to C₆ divalent saturated hydrocarbon group.

L^(b15) is preferably a single bond or a C₁ to C₁₈ divalent saturated hydrocarbon group, and more preferably a single bond or a C₁ to C₈ divalent saturated hydrocarbon group.

L^(b16) is preferably a C₁ to C₁₂ divalent saturated hydrocarbon group.

L^(b17) is preferably a C₁ to C₆ divalent saturated hydrocarbon group.

L^(b18) is preferably a single bond or a C₁ to C₁₇ divalent saturated hydrocarbon group, and more preferably a single bond or a C₁ to C₄ divalent saturated hydrocarbon group.

Examples of the divalent group represented by the formula (b1-3) include the following groups represented by formula (b1-9) to formula (b1-11):

wherein L^(b19) represents a single bond or a C₁ to C₂₃ divalent saturated hydrocarbon group where a hydrogen atom may be replaced by a fluorine atom;

L^(b20) represent a single bond or a C₁ to C₂₃ divalent saturated hydrocarbon group where a hydrogen atom may be replaced by a fluorine atom, a hydroxy group or an acyloxy group, and a methylene group contained in an acyloxy group may be replaced by an oxygen atom or a carbonyl group, and a hydrogen atom contained in an acyloxy group may be replaced by a hydroxy group,

provided that the total carbon number contained in the group of L^(b19) and L^(b20) is 23 or less;

L^(b21) represents a single bond or a C₁ to C₂₁ divalent saturated hydrocarbon group where a hydrogen atom may be replaced by a fluorine atom;

L^(b22) represents a single bond or a C₁ to C₂₁ divalent saturated hydrocarbon group;

L^(b23) represents a single bond or a C₁ to C₂₁ divalent saturated hydrocarbon group where a hydrogen atom may be replaced by a fluorine atom, a hydroxy group or an acyloxy group, and a methylene group contained in an acyloxy group may be replaced by an oxygen atom or a carbonyl group, and a hydrogen atom contained in an acyloxy group may be replaced by a hydroxy group,

provided that the total carbon number contained in the group of L^(b21), L^(b22) and L^(b23) is 21 or less;

L^(b24) represents a single bond or a C₁ to C₂₀ divalent saturated hydrocarbon group where a hydrogen atom may be replaced by a fluorine atom;

L^(b25) represents a single bond or a C₁ to C₂₁ divalent saturated hydrocarbon group;

L^(b26) represents a single bond or a C₁ to C₂₀ divalent saturated hydrocarbon group where a hydrogen atom may be replaced by a fluorine atom, a hydroxy group or an acyloxy group, and a methylene group contained in an acyloxy group may be replaced by an oxygen atom or a carbonyl group, and a hydrogen atom contained in an acyloxy group may be replaced by a hydroxy group,

provided that the total carbon number contained in the group of L^(b24), L^(b25) and L^(b26) is 21 or less.

In formula (b1-9) to formula (b1-11), when a hydrogen atom has been replaced by an acyloxy group, the carbon number of the saturated hydrocarbon group corresponds to the number of the carbon atom, CO and O in addition to the carbon number of the saturated hydrocarbon group.

For formula (b1-9) to formula (b1-11), examples of the divalent saturated hydrocarbon group include an alkanediyl and a monocyclic or polycyclic divalent saturated hydrocarbon group, and a combination of two or more such groups.

Examples of the acyloxy group include acetyloxy, propionyloxy, butyryloxy, cyclohexyl carbonyloxy and adamantyl carbonyloxy groups.

Examples of the acyloxy group having a substituent include oxoadamantyl carbonyloxy, hydroxyadamantyl carbonyloxy, oxocyclohexyl carbonyloxy and hydroxycyclohexyl carbonyloxy groups.

Examples of the group represented by the formula (b1-4) include the following ones.

Examples of the group represented by the formula (b1-5) include the following ones.

Examples of the group represented by the formula (b1-6) include the following ones.

Examples of the group represented by the formula (b1-7) include the following ones.

Examples of the group represented by the formula (b1-8) include the following ones.

Examples of the group represented by the formula (b1-2) include the following ones.

Examples of the group represented by the formula (b1-9) include the following ones.

Examples of the group represented by the formula (b1-10) include the following ones.

Examples of the group represented by the formula (b1-11) include the following ones.

Examples of the monovalent alicyclic hydrocarbon group of Y include groups represented by formula (Y1) to formula (Y11).

Examples of the monovalent alicyclic hydrocarbon group of Y in which a methylene group has been replaced by an oxygen atom, a carbonyl group or a sulfonyl group include groups represented by formula (Y12) to formula (Y27).

Among these, the alicyclic hydrocarbon group is preferably any one of groups represented by the formula (Y1) to the formula (Y19), more preferably any one of groups represented by the formula (Y11), (Y14), (Y15) or (Y19), and still more preferably group represented by the formula (Y11) or (Y14).

Examples of the substituent for the alicyclic group of Y include a halogen atom, a hydroxyl group, a C₁ to C₁₂ alkyl group, a hydroxy group-containing C₁ to C₁₂ alkyl group, a C₃ to C₁₆ monovalent alicyclic hydrocarbon group, a C₁ to C₁₂ alkoxy group, a C₆ to C₁₈ monovalent aromatic hydrocarbon group, a C₇ to C₂₁ aralkyl group, a C₂ to C₄ acyl group, a glycidyloxy group and —(CH₂)_(j2)—O—CO—R^(b1)— in which R^(b1) represents an C₁ to C₁₆ alkyl group, a C₃ to C₁₆ monovalent alicyclic hydrocarbon group, or a C₆ to C₁₈ monovalent aromatic hydrocarbon group, and j2 represents an integer of 0 to 4.

Examples of the hydroxy group-containing alkyl group include hydroxymethyl and hydroxyethyl groups

Examples of the alkoxyl group include methoxy, ethoxy, propoxy, butoxy, pentyloxy, hexyloxy, heptyloxy, octyloxy, decyloxy and dodecyloxy groups.

Examples of the monovalent aromatic hydrocarbon group include an aryl group such as phenyl, naphthyl, anthryl, p-methylphenyl, p-tert-butylphenyl, p-adamantylphenyl, tolyl, xylyl, cumenyl, mesityl, biphenyl, phenanthryl, 2,6-diethylphenyl and 2-methyl-6-ethylphenyl groups.

Examples of the aralkyl group include benzyl, phenethyl, phenylpropyl, naphthylmethyl and naphthylethyl groups.

Examples of the acyl group include acetyl, propionyl and butyryl groups.

Examples of the halogen atom include fluorine, chlorine, bromine and iodine atoms.

Examples of Y include the groups below. * represents a binding site to L^(b1).

Y is preferably a C₃ to C₁₈ monovalent alicyclic hydrocarbon group which may have a substituent, more preferably an adamantyl group which may have a substituent and one or more methylene group contained in the adamantyl group may be replaced with an oxygen atom, a carbonyl group or a sulfonyl group, and still more preferably an adamantyl group, a hydroxyadamantyl group or an oxoadamantyl group.

The sulfonic acid anion in the salt represented by the formula (B1) is preferably an anions represented by formula (B1-A-1) to formula (B1-A-33), and more preferably an anions represented by formula (B1-A-1) to formula (B1-A-4), formula (B1-A-9), formula (B1-A-10), formula (B1-A-24) to formula (B1-A-33), below.

In the formula (B1-A-1) to the formula (B1-A-33), R^(i2) to R^(i7) independently represent, for example, a C₁ to C₄ alkyl group, and preferably methyl or ethyl group, R^(i8) represent, for example, a C₁ to C₁₂ aliphatic hydrocarbon group, preferably a C₁ to C₄ alkyl group, a C₅ to C₁₂ monovalent alicyclic hydrocarbon group or a group formed by a combination thereof, more preferably a methyl, ethyl group, cyclohexyl group or adamantyl group. L⁴⁴ represents a single bond or a C₁ to C₄ alkanediyl group. Q¹ and Q² represent the same meaning as defined above.

Specific examples of the sulfonic acid anion in the salt represented by the formula (B1) include anions mentioned in JP2010-204646A1.

Among these, preferred examples of the sulfonic acid anion for the salt represented by the formula (B1) include anions represented by formulae (B1a-1) to (B1a-15).

Among them, preferred examples of the sulfonic acid anion include anions represented by the formulae (B1a-1) to (B1a-3) and (B1a-7) to (B1a-15).

Examples of the organic cation represented by Z⁺ include an organic onium cation such as an organic sulfonium cation, an organic iodonium cation, an organic ammonium cation, a benzothiazolium cation and an organic phosphonium cation, and an organic sulfonium cation and an organic iodonium cation are preferred, and an arylsulfonium cation is more preferred.

Z⁺ of the formula (B1) is preferably represented by any of the formula (b2-1) to the formula (b2-4):

wherein R^(b4), R^(b5) and R^(b6) independently represent a C₁ to C₃₀ aliphatic hydrocarbon group, a C₃ to C₃₆ alicyclic hydrocarbon group or a C₆ to C₃₆ aromatic hydrocarbon group, a hydrogen atom contained in an aliphatic hydrocarbon group may be replaced by a hydroxy group, a C₁ to C₁₂ alkoxy group, a C₃ to C₁₂ alicyclic hydrocarbon group or a C₆ to C₁₈ aromatic hydrocarbon group, a hydrogen atom contained in an alicyclic hydrocarbon group may be replaced by a halogen atom, a C₁ to C₁₈ aliphatic hydrocarbon group, a C₂ to C₄ acyl group or a glycidyloxy group, a hydrogen atom contained in an aromatic hydrocarbon group may be replaced by a halogen atom, a hydroxy group or a C₁ to C₁₂ alkoxy group, or R^(b4) and R^(b5) may be bonded together with a sulfur atom bonded thereto to form a sulfur-containing ring, a methylene group contained in the ring may be replaced by an oxygen atom, a —SO— or a carbonyl group;

R^(b7) and R^(b8) in each occurrence independently represent a hydroxy group, a C₁ to C₁₂ aliphatic hydrocarbon group or a C₁ to C₁₂ alkoxy group,

m2 and n2 independently represent an integer of 0 to 5;

R^(b9) and R^(b10) each independently represent a C₁ to C₃₆ aliphatic hydrocarbon group or a C₃ to C₃₆ alicyclic hydrocarbon group, or R^(b9) and R^(b10) may be bonded together with a sulfur atom bonded thereto to form a sulfur-containing ring, and a methylene group contained in the ring may be replaced by an oxygen atom, a —SO— or a carbonyl group;

R^(b11) represents a hydrogen atom, a C₁ to C₃₆ aliphatic hydrocarbon group, a C₃ to C₃₆ alicyclic hydrocarbon group or a C₆ to C₁₈ aromatic hydrocarbon group;

R^(b12) represents a C₁ to C₁₂ aliphatic hydrocarbon group, a C₃ to C₁₈ alicyclic hydrocarbon group and a C₆ to C₁₈ aromatic hydrocarbon group, a hydrogen atom contained in an aliphatic hydrocarbon group may be replaced by a C₆ to C₁₈ aromatic hydrocarbon group, and a hydrogen atom contained in an aromatic hydrocarbon group may be replaced by a C₁ to C₁₂ alkoxy group or a C₁ to C₁₂ alkyl carbonyloxy group;

R^(b11) and R^(b12) may be bonded together with —CH—CO— bonded thereto to form a ring, and a methylene group contained in the ring may be replaced by an oxygen atom, a —SO— or a carbonyl group;

R^(b13), R^(b14), R^(b15), R^(b16), R^(b17) and R^(b18) in each occurrence independently represent a hydroxy group, a C₁ to C₁₂ aliphatic hydrocarbon group or a C₁ to C₁₂ alkoxy group;

L^(b11) represents —S— or —O—;

o2, p2, s2 and t2 independently represent an integer of 0 to 5;

q2 or r2 independently represent an integer of 0 to 4; and

u2 represents an integer of 0 or 1.

Examples of the aliphatic group preferably include methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, tert-butyl, n-pentyl, n-hexyl, n-octyl and 2-ethylhexyl groups. Among these, the aliphatic hydrocarbon group of R^(b9) to R^(b12) is preferably a C₁ to C₁₂ aliphatic hydrocarbon group.

Examples of the alicyclic hydrocarbon group preferably include monocyclic groups such as a cycloalkyl group, i.e., cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, cyclodecyl groups; and polycyclic groups such as decahydronaphtyl, adamantyl and norbornyl groups as well as the following groups. * represents a binding site.

Among these, the alicyclic hydrocarbon group of R^(b9) to R^(b12) is preferably a C₃ to C₁₈ alicyclic hydrocarbon group, and more preferably a C₄ to C₁₂ alicyclic hydrocarbon group.

Examples of the alicyclic hydrocarbon group where a hydrogen atom may be replaced by an aliphatic hydrocarbon group include methylcyclohexyl, dimethylcyclohexyl, 2-alkyladamantane-2-yl, methylnorbornyl and isobornyl groups. In the alicyclic hydrocarbon group where a hydrogen atom may be replaced by an aliphatic hydrocarbon group, the total carbon number of the alicyclic hydrocarbon group and the aliphatic hydrocarbon group is preferably 20 or less.

Examples of the aromatic hydrocarbon group preferably include an aryl group such as phenyl, tolyl, xylyl, cumenyl, mesityl, p-ethylphenyl, p-tert-butylphenyl, p-cyclohexylphenyl, p-adamantylphenyl, biphenyl, naphthyl, phenanthryl, 2,6-diethylphenyl and 2-methyl-6-ethylphenyl groups.

When the aromatic hydrocarbon includes an aliphatic hydrocarbon group or an alicyclic hydrocarbon group, a C₁ to C₁₈ aliphatic hydrocarbon group or a C₃ to C₁₈ alicyclic hydrocarbon group is preferred.

Examples of the aromatic hydrocarbon group where a hydrogen atom may be replaced by an alkoxy group include a p-methoxyphenyl group.

Examples of the aliphatic hydrocarbon group where a hydrogen atom may be replaced by an aromatic hydrocarbon group include an aralkyl group such as benzyl, phenethyl phenylpropyl, trityl, naphthylmethyl and naphthylethyl groups.

Examples of the alkoxy group include methoxy, ethoxy, propoxy, butoxy, pentyloxy, hexyloxy, heptyloxy, octyloxy, and dodecyloxy groups.

Examples of the acyl group include acetyl, propionyl and butyryl groups.

Examples of the halogen atom include fluorine, chlorine, bromine and iodine atoms.

Examples of the alkylcarbonyloxy group include methylcarbonyloxy, ethylcarbonyloxy, n-propylcarbonyloxy, isopropylcarbonyloxy, n-butylcarbonyloxy, sec-butylcarbonyloxy, tert-butyl carbonyloxy, pentylcarbonyloxy, hexylcarbonyloxy, octylcarbonyloxy and 2-ethylhexylcarobonyloxy groups.

The sulfur atom-containing ring which is formed by R^(b4) and R^(b5) may be a monocyclic or polycyclic group, which may be an aromatic or non-aromatic group, and which may be a saturated or unsaturated group. The ring is preferably a ring having 3 to 18 carbon atoms, and more preferably a ring having 4 to 13 carbon atoms. Examples of the sulfur atom-containing ring include a 3- to 12-membered ring, preferably a 3- to 7-membered ring, examples thereof include the following rings.

Examples of the ring formed by R^(b9) and R^(b10) may be any of monocyclic, polycyclic, aromatic, non-aromatic, saturated and unsaturated rings. The ring may be a 3- to 12-membered ring, preferably a 3- to 7-membered ring. Examples of the ring include thiolane-1-ium ring (tetrahydrothiophenium ring), thian-1-ium ring and 1,4-oxathian-4-ium ring.

Examples of the ring formed by R^(b11) and R^(b12) may be any of monocyclic, polycyclic, aromatic, non-aromatic, saturated and unsaturated rings. The ring may be a 3- to 12-membered ring, preferably a 3- to 7-membered ring. Examples of the ring include oxocycloheptane ring, oxocyclohexane ring, oxonorbornane ring and oxoadamantane ring.

Among the cations represented by the formula (b2-1) to the formula (b2-4), the cation represented by the formula (b2-1) is preferred.

Examples of the cation (b2-1) include the following ones.

Examples of the cation (b2-2) include the following ones.

Examples of the cation (b2-3) include the following ones.

Examples of the cation (b2-4) include the following ones.

Preferred acid generators (B1) are represented by the formula (B1-1) to the formula (B1-30). Among these, the formulae (B1-1), (B1-2), (B1-3), (B1-5), (B1-6), (B1-7), (B1-11), (B1-12), (B1-13), (B1-14), (B1-17), (B1-20), (B1-21), (B1-23), (B1-24), (B1-25), (B1-26) and (B1-29) which contain arylsulfonium cation are preferred.

The proportion of the acid generator (B1) is preferably 30% by mass or more, and 100% by mass or less, more preferably 50% by mass or more, and 100% by mass or less, and still more preferably substantially 100% by weight with respect to 100% by mass of total acid generator (B).

In the resist composition of the disclosure, the proportion of the acid generator (B) is preferably 1 parts by mass or more and more preferably 3 parts by mass or more, and preferably 30 parts by mass or less and more preferably 25 parts by mass or less with respect to 100 parts by mass of the resin (A1).

In the resist composition of the disclosure, the acid generator (B) may be used as a single salt or as a combination of two or more of salts.

<Solvent (E)>

The proportion of a solvent (E) is generally 90% by mass or more, preferably 92% by mass or more, and more preferably 94% by mass or more, and also preferably 99% by mass or less, and more preferably 99.9% by mass or less. The proportion of the solvent (E) can be measured with a known analytical method such as liquid chromatography and gas chromatography.

Examples of the solvent (E) include glycol ether esters such as ethylcellosolve acetate, methylcellosolve acetate and propyleneglycolmonomethylether acetate; glycol ethers such as propylene glycol monomethyl ether; esters such as ethyl lactate, butyl acetate, amyl acetate and ethyl pyruvate; ketones such as acetone, methyl isobutyl ketone, 2-heptanone and cyclohexanone; and cyclic esters such as α-butyrolactone. These solvents may be used as a single solvent or as a mixture of two or more solvents.

<Quencher (C)>

The resist composition of the disclosure may contain a quencher such as a basic nitrogen-containing organic compound and a salt which generates an acid weaker in acidity than an acid generated from the acid generator.

The proportion of the quencher is preferably 0.01% by mass to 5% by mass with respect to the total solid components of the resist composition.

Examples of the basic nitrogen-containing organic compound include an amine and ammonium salts. The amine may be an aliphatic amine or an aromatic amine. The aliphatic amine includes any of a primary amine, secondary amine and tertiary amine.

Specific examples of the amine include 1-naphtylamine, 2-naphtylamine, aniline, diisopropylaniline, 2-, 3- or 4-methylaniline, 4-nitroaniline, N-methylaniline, N,N-dimethylaniline, diphenylamine, hexylamine, heptylamine, octylamine, nonylamine, decylamine, dibutylamine, dipentylamine, dihexylamine, diheptylamine, dioctylamine, dinonylamine, didecylamine, triethylamine, trimethylamine, tripropylamine, tributylamine, tripentylamine, trihexylamine, triheptylamine, trioctylamine, trinonylamine, tridecylamine, methyldibutylamine, methyldipentylamine, methyldihexylamine, methyldicyclohexylamine, methyldiheptylamine, methyldioctylamine, methyldinonylamine, methyldidecylamine, ethyldibutylamine, ethyldipentylamine, ethyldihexylamine, ethyldiheptylamine, ethyldioctylamine, ethyldinonylamine, ethyldidecylamine, dicyclohexylmethylamine, tris[2-(2-methoxyethoxy)ethyl]amine, triisopropanolamine, ethylene diamine, tetramethylene diamine, hexamethylene diamine, 4,4′-diamino-1,2-diphenylethane, 4,4′-diamino-3,3′-dimethyldiphenylmethane, 4,4′-diamino-3,3′-diethyldiphenylmethane, 2,2′-methylenebisaniline, imidazole, 4-methylimidazole, pyridine, 4-methylpyridine, 1,2-di(2-pyridyl)ethane, 1,2-di(4-pyridyl)ethane, 1,2-di(2-pyridyl)ethene, 1,2-di(4-pyridyl)ethene, 1,3-di(4-pyridyl)propane, 1,2-di(4-pyridyloxy)ethane, di(2-pyridyl)ketone, 4,4′-dipyridyl sulfide, 4,4′-dipyridyl disulfide, 2,2′-dipyridylamine, 2,2′-dipicolylamine and bipyridine. Among these, diisopropylaniline is preferred, particularly 2,6-diisopropylaniline is more preferred.

Specific examples of the ammonium salt include tetramethylammonium hydroxide, tetraisopropylammonium hydroxide, tetrabutylammonium hydroxide, tetrahexylammonium hydroxide, tetraoctylammonium hydroxide, phenyltrimethyl ammonium hydroxide, 3-(trifluoromethyl)phenyltrimethylammonium hydroxide, tetra-n-butyl ammonium salicylate and choline.

<Weak Acid Salt>

The salt generating an acid which is lower in acidity than an acid generated from the acid generator (B) is sometimes referred to as “weak acid salt”. The “acidity” can be represented by acid dissociation constant, pKa, of an acid generated from a weak acid salt. Examples of the weak acid salt include a salt generating an acid of pKa represents generally more than −3, preferably −1 to 7, and more preferably 0 to 5.

Specific examples of the weak acid salt include the following salts, the salt of formula (D), and salts as disclosed in JP2012-229206A1, JP2012-6908A1, JP2012-72109A1, JP2011-39502A1 and JP2011-191745A1, preferably the salt of formula (D).

In the formula (D), R^(D1) and R^(D2) in each occurrence independently represent a C₁ to C₁₂ hydrocarbon group, a C₁ to C₆ alkoxyl group, a C₂ to C₇ acyl group, a C₂ to C₇ acyloxy group, a C₂ to C₇ alkoxycarbonyl group, a nitro group or a halogen atom;

m′ and n′ each independently represent an integer of 0 to 4.

Examples of the hydrocarbon group of R^(D1) and R^(D2) include any of an aliphatic hydrocarbon group, an alicyclic hydrocarbon group, an aromatic hydrocarbon group and a combination thereof.

Examples of the aliphatic hydrocarbon group include an alkyl group such as methyl, ethyl, propyl, isopropyl, butyl, sec-butyl, tert-butyl, pentyl, hexyl and nonyl groups.

The alicyclic hydrocarbon group is any one of monocyclic or polycyclic hydrocarbon group, and saturated or unsaturated hydrocarbon group. Examples thereof include a cycloalkyl group such as cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cyclononyl and cyclododecyl groups; adamantyl and norbornyl groups. The alicyclic hydrocarbon group is preferably saturated hydrocarbon group.

Examples of the aromatic hydrocarbon group include an aryl group such as phenyl, 1-naphthyl, 2-naphthyl, 2-methylphenyl, 3-methylphenyl, 4-methylphenyl, 4-ethylphenyl, 4-propylphenyl, 4-isopropylphenyl, 4-butylphenyl, 4-tert-butylphenyl, 4-hexylphenyl, 4-cyclohexylphenyl, anthryl, p-adamantylphenyl, tolyl, xylyl, cumenyl, mesityl, biphenyl, phenanthryl, 2,6-diethylphenyl and 2-methyl-6-ethylphenyl groups.

Examples of the combination thereof include an alkyl-cycloalkyl, a cycloalkyl-alkyl, aralkyl (e.g., phenylmethyl, 1-phenylethyl, 2-phenylethyl, 1-phenyl-1-propyl, 1-phenyl-2-propyl, 2-phenyl-2-propyl, 3-phenyl-1-propyl, 4-phenyl-1-butyl, 5-phenyl-1-pentyl and 6-phenyl-1-hexyl groups) groups.

Examples of the alkoxyl group include methoxy and ethoxy groups.

Examples of the acyl group include acetyl, propanonyl, benzoyl and cyclohexanecarbonyl groups.

Examples of the acyloxy group include a group in which oxy group (—O—) bonds to an acyl group.

Examples of the alkoxycarbonyl group include a group in which the carbonyl group (—CO—) bonds to the alkoxy group.

Example of the halogen atom is a chlorine atom, a fluorine atom and bromine atom.

In the formula (D), R^(D1) and R^(D2) in each occurrence independently preferably represent a C₁ to C₈ alkyl group, a C₃ to C₁₀ cycloalkyl group, a C₁ to C₆ alkoxyl group, a C₂ to C₄ acyl group, a C₂ to C₄ acyloxy group, a C₂ to C₄ alkoxycarbonyl group, a nitro group or a halogen atom.

m′ and n′ independently preferably represent an integer of 0 to 3, more preferably an integer of 0 to 2, and more preferably 0.

Specific examples of the salt of the formula (D) include compounds below.

The salt of the formula (D) can be produced by a method described in “Tetrahedron Vol. 45, No. 19, p6281-6296”. Also, commercially available compounds can be used as the salt of the formula (D).

In the resist composition of the disclosure, the proportion of the salt which generates an acid weaker in acidity than an acid generated from the acid generator, for example, the salt of the formula (D) is preferably 0.01% by mass to 5% by mass, more preferably 0.01% by mass to 4% by mass, and still more preferably 0.01% by mass to 3% by mass with respect to total solid components of the resist composition.

<Other Ingredient>

The resist composition can also include other ingredient (which is sometimes referred to as “other ingredient (F)”). Examples of the other ingredient (F) include various additives such as sensitizers, dissolution inhibitors, surfactants, stabilizers, and dyes, as needed.

<Preparing the Resist Composition>

The present resist composition can be prepared by mixing the resins (A1) and (A2), the acid generator (B), the resin other than the resin (A), the quencher, the solvent (E) and the other ingredient (F), as needed. There is no particular limitation on the order of mixing. The mixing may be performed in an arbitrary order. The temperature of mixing may be adjusted to an appropriate temperature within the range of 10 to 40° C., depending on the kinds of the resin and solubility in the solvent (E) of the resin. The time of mixing may be adjusted to an appropriate time within the range of 0.5 to 24 hours, depending on the mixing temperature. There is no particular limitation to the tool for mixing. An agitation mixing may be used.

After mixing the above ingredients, the present resist compositions can be prepared by filtering the mixture through a filter having about 0.003 to 0.2 μm pore diameter.

<Method for Producing Resist Pattern>

The method for producing a resist pattern of the disclosure includes the steps of:

(1) applying the resist composition of the disclosure onto a substrate;

(2) drying the applied composition to form a composition layer;

(3) exposing the composition layer;

(4) heating the exposed composition layer, and

(5) developing the heated composition layer.

Applying the resist composition onto the substrate can generally be carried out through the use of a resist application device, such as a spin coater known in the field of semiconductor microfabrication technique. Examples of the substrate include inorganic substrates such as silicon wafer. The substrate may be washed, and an organic antireflection film may be formed on the substrate by use of a commercially available antireflection composition, before the application of the resist composition.

The solvent evaporates from the resist composition and a composition layer with the solvent removed is formed. Drying the applied composition layer, for example, can be carried out using a heating device such as a hotplate (so-called “prebake”), a decompression device, or a combination thereof. The temperature is preferably within the range of 50 to 200° C. The time for heating is preferably 10 to 180 seconds. The pressure is preferably within the range of 1 to 1.0×10⁵ Pa.

The obtained composition layer is generally exposed using an exposure apparatus or a liquid immersion exposure apparatus. The exposure is generally carried out using with various types of exposure light source, such as irradiation with ultraviolet lasers, i.e., KrF excimer laser (wavelength: 248 nm), ArF excimer laser (wavelength: 193 nm), F₂ excimer laser (wavelength: 157 nm), irradiation with harmonic laser light of far-ultraviolet or vacuum ultra violet wavelength-converted laser light from a solid-state laser source (YAG or semiconductor laser or the like), or irradiation with electron beam or EUV or the like. In the specification, such exposure to radiation is sometimes referred to be collectively called as exposure. The exposure is generally carried out through a mask that corresponds to the desired pattern. When electron beam is used as the exposure light source, direct writing without using a mask can be carried out.

After exposure, the composition layer is subjected to a heat treatment (so-called “post-exposure bake”) to promote the deprotection reaction. The heat treatment can be carried out using a heating device such as a hotplate. The heating temperature is generally in the range of 50 to 200° C., preferably in the range of 70 to 150° C.

The developing of the baked composition film is usually carried out with a developer using a development apparatus. Developing can be conducted in the manner of dipping method, paddle method, spray method and dynamic dispensing method. Temperature for developing is generally 5 to 60° C. The time for developing is preferably 5 to 300 seconds.

The photoresist pattern obtained from the photoresist composition may be a positive one or a negative one by selecting suitable developer.

The development for obtaining a positive photoresist pattern is usually carried out with an alkaline developer. The alkaline developer to be used may be any one of various alkaline aqueous solution used in the art. Generally, an aqueous solution of tetramethylammonium hydroxide or (2-hydroxyethyl)trimethylammonium hydroxide (commonly known as “choline”) is often used. The surfactant may be contained in the alkaline developer.

After development, the resist pattern formed is preferably washed with ultrapure water, and the residual water remained on the resist film or on the substrate is preferably removed therefrom.

The development for obtaining a negative photoresist pattern is usually carried out with a developer containing an organic solvent. The organic solvent to be used may be any one of various organic solvents used in the art, examples of which include ketone solvents such as 2-hexanone, 2-heptanone; glycol ether ester solvents such as propyleneglycolmonomethylether acetate; ester solvents such as the butyl acetate; glycol ether solvents such as the propyleneglycolmonomethylether; amide solvents such as N,N-dimethylacetamide; aromatic hydrocarbon solvents such as anisole.

In the developer containing an organic solvent, the amount of organic solvents is preferably 90% by mass to 100% by mass, more preferably 95% by mass to 100% by mass of the developer. The developer still more preferably consists essentially of organic solvents.

Among these, the developer containing an organic solvent preferably contains butyl acetate and/or 2-heptanone. In the developer containing an organic solvent, the total amount of butyl acetate and 2-heptanone is preferably 50% by mass to 100% by mass of the developer, more preferably 90% by mass to 100% by mass of the developer. The developer still more preferably consists essentially of butyl acetate and/or 2-heptanone.

Developers containing an organic solvent may contain a surfactant. Also, the developer containing an organic solvent may include a little water.

The developing with a developer containing an organic solvent can be finished by replacing the developer by another solvent.

After development, the photoresist pattern formed is preferably washed with a rinse agent. Such rinse agent is not unlimited provided that it does not detract a photoresist pattern. Examples of the agent include solvents which contain organic solvents other than the above-mentioned developers, such as alcohol agents or ester agents.

After washing, the residual rinse agent remained on the substrate or photoresist film is preferably removed therefrom.

<Application>

The resist composition of the disclosure is useful for excimer laser lithography such as ArF, KrF, electron beam (EB) exposure lithography or extreme-ultraviolet (EUV) exposure lithography, and is more useful for ArF excimer laser exposure lithography.

The resist composition of the disclosure can be used in semiconductor microfabrication.

EXAMPLES

The disclosure will be described more specifically by way of examples, which are not construed to limit the scope of the disclosure.

All percentages and parts expressing the content or amounts used in the Examples and Comparative Examples are based on mass, unless otherwise specified.

The weight average molecular weight is a value determined by gel permeation chromatography.

Column: TSK gel Multipore HXL-M×3+guardcolumn (Tosoh Co. Ltd.)

Eluant: tetrahydrofuran

Flow rate: 1.0 mL/min

Detecting device: RI detector

Column temperature: 40° C.

Injection amount: 100 μL

Standard material for calculating molecular weight: standard polystyrene (Tosoh Co. ltd.)

Structures of compounds were determined by mass spectrometry (Liquid Chromatography: 1100 Type, manufactured by AGILENT TECHNOLOGIES LTD., Mass Spectrometry: LC/MSD Type, manufactured by AGILENT TECHNOLOGIES LTD.). The value of the peak in the mass spectrometry is referred to as “MASS”.

Synthesis Example 1: Synthesis of the Salt Represented by the Formula (B1-5)

Into a reactor, 50.49 parts of compound represented by the formula (B1-5-a) and 252.44 parts of chloroform were charged and stirred at 23° C. for 30 minutes. Then 16.27 parts of compound represented by the formula (B1-5-b) were dropped thereinto and the obtained mixture was stirred at 23° C. for one hour to obtain a solution containing a salt represented by the formula (B1-5-c). To the obtained solution, 48.80 parts of a salt represented by the formula (B1-5-d) and 84.15 parts of ion-exchanged water were added and the obtained mixture was stirred at 23° C. for 12 hours. From the obtained solution which had two layers, the chloroform layer was collected and then 84.15 parts of ion-exchanged water were added thereto for washing. The washing with water step was conducted five times. To the washed chloroform layer, 3.88 parts of active carbon was added and the obtained mixture was stirred, followed by filtrating. The collected filtrate was concentrated and then 125.87 parts of acetonitrile were added thereto and the obtained mixture was stirred, followed by being concentrated. 20.62 parts of acetonitrile and 309.30 parts of tert-butyl methyl ether were added to the obtained residues, followed by being stirred at 23° C. for about 30 minutes. Then the supernatant was removed therefrom, and the residues were concentrated. To the concentrated residues, 200 parts of n-heptane were added and the obtained mixture was stirred at 23° C. for about 30 minutes, followed by being filtrated whereby giving 61.54 parts of the salt represented by the formula (B1-5).

MASS(ESI(+)Spectrum):M+ 375.2

MASS(ESI(−)Spectrum):M− 339.1

Synthesis Example 2: Synthesis of the Salt Represented by the Formula (B1-21)

The compound represented by the formula (B1-21-b) was produced according to a method recited in JP2008-209917A1.

Into a reactor, 30.00 parts of compound represented by the formula (B1-21-b) and 35.50 parts of salt represented by the formula (B1-21-a), 100 parts of chloroform and 50 parts of ion exchanged water were charged and stirred at 23° C. for about 15 hours. The obtained reaction mixture, which had two layers, was separated into a chloroform layer therefrom. To the chloroform layer, 30 parts of ion exchanged water was added and washed with it. These steps were conducted five times. Then the washed layer was concentrated, and then, 100 parts of tert-butyl methyl ether was added to the obtained residues and the obtained mixture was stirred at 23° C. for about 30 minutes. The resulting mixture was filtrated to obtain 48.57 parts of salt represented by the formula (B1-21-c).

Into a reactor, 20.00 parts of salt represented by the formula (B1-21-c), 2.84 parts of compound represented by the formula (B1-21-d) and 250 parts of monochlorobenzene were charged and stirred at 23° C. for 30 minutes. To the resulting mixture, 0.21 parts of copper (II) dibenzoate was added and the obtained mixture was stirred at 100° C. for 1 hour. The reaction mixture was concentrated, and then, 200 parts of chloroform and 50 parts of ion exchanged water were added to the obtained residues and the obtained mixture was stirred at 23° C. for 30 minutes, followed by separating an organic layer to wash with water. 50 parts of ion exchanged water was added to the obtained organic layer, and the obtained mixture was stirred at 23° C. for 30 minutes, followed by separating an organic layer. The washing step with water was conducted five times. The obtained organic layer was concentrated, and then the obtained residues were dissolved in 53.51 parts of acetonitrile. Then the mixture was concentrated, and then 113.05 parts of tert-butyl methyl ether was added thereto and the obtained mixture was stirred, followed by filtrating it to obtain 10.47 parts of the salt represented by the formula (B1-21).

MASS(ESI(+)Spectrum):M+ 237.1

MASS(ESI(−)Spectrum):M− 339.1

Synthesis Example 3: Synthesis of the Salt Represented by the Formula (B1-22)

Into a reactor, 11.26 parts of salt represented by the formula (B1-21-a), 10 parts of compound represented by the formula (B1-22-b), 50 parts of chloroform and 25 parts of ion exchanged water were charged and stirred at 23° C. for about 15 hours. The obtained reaction mixture, which had two layers, was separated into a chloroform layer therefrom. To the chloroform layer, 15 parts of ion exchanged water were added and washed with it: These steps were conducted five times. Then the washed layer was concentrated, and then 50 parts of tert-butyl methyl ether was added to the obtained residues, and the obtained mixture was stirred at 23° C. for about 30 minutes. The resulting mixture was filtrated to obtain 11.75 parts of the salt represented by the formula (B1-22-c).

Into a reactor, 11.71 parts of a salt represented by the formula (B1-22-c), 1.70 parts of a compound represented by the formula (B1-21-d) and 46.84 parts of monochlorobenzene were charged and stirred at 23° C. for 30 minutes. To the resulting mixture, 0.12 parts of copper (II) dibenzoate was added and the obtained mixture was stirred at 100° C. for 30 minutes. The reaction mixture was concentrated, and then 50 parts of chloroform and 12.50 parts of ion exchanged water were added to the obtained residues, and the obtained mixture was stirred at 23° C. for 30 minutes, followed by separating an organic layer to wash with water. 12.50 parts of ion exchanged water was added to the obtained organic layer and the obtained mixture was stirred at 23° C. for 30 minutes, followed by separating an organic layer to wash with water. The washing step with water was conducted eight times. Then the obtained organic layer was concentrated, and then 50 parts of tert-butyl methyl ether were added thereto and the obtained mixture was stirred, followed by filtrating it to obtain 6.84 parts of the salt represented by the formula (B1-22).

MASS(ESI(+)Spectrum):M+ 237.1

MASS(ESI(−)Spectrum):M− 323.0

Synthesis Examples of Resins

The monomers used for Synthesis Examples of the resins are shown below. These monomers are referred to as “monomer (X)” where “(X)” is the symbol of the formula representing the structure of each monomer.

Example 1: Synthesis of Resin A1-1

Monomer (a4-0-1), monomer (1-2) and monomer (a3-4′-8) were mixed together with the mole ratio of monomer (a4-0-1), monomer (1-2) and monomer (a3-4′-8)=50:35:15, and propyleneglycolmonomethylether acetate was added thereto in the amount equal to 1.2 times by mass of the total amount of monomers to obtain a solution. Azobisisobutyronitrile and azobis(2,4-dimethylvaleronitrile) were added as initiators to the solution in the amounts of 0.85% by mole and 2.55% by mole respectively with respect to the total amount of monomers, and the resultant mixture was heated for about 5 hours at 75° C. Then, the obtained reaction mixture was poured into a large amount of a mixture of methanol and ion exchanged water to precipitate a resin. The obtained resin was filtrated. The obtained resin was poured into another methanol to wash. The obtained resin was filtrated to obtain the copolymer having a weight average molecular weight of about 12000 in 92% yield. This resin, which had the structural units of the following formula, was referred to Resin A1-1.

Example 2: Synthesis of Resin A1-2

Monomer (a4-0-12), monomer (I-1) and monomer (a3-4′-8) were mixed together with the mole ratio of monomer (a4-0-12), monomer (I-1) and monomer (a3-4′-8)=50:45:5, and propyleneglycolmonomethylether acetate was added thereto in the amount equal to 1.2 times by mass of the total amount of monomers to obtain a solution. Azobisisobutyronitrile and azobis(2,4-dimethylvaleronitrile) were added as initiators to the solution in the amounts of 0.85% by mole and 2.55% by mole respectively with respect to the total amount of monomers, and the resultant mixture was heated for about 5 hours at 75° C. Then, the obtained reaction mixture was poured into a large amount of a mixture of methanol and ion exchanged water to precipitate a resin. The obtained resin was filtrated. The obtained resin was poured into another methanol to wash. The obtained resin was filtrated to obtain the copolymer having a weight average molecular weight of about 13000 in 85% yield. This resin, which had the structural units of the following formula, was referred to Resin A1-2.

Example 3: Synthesis of Resin A1-3

Monomer (a4-0-2), monomer (I-1) and monomer (a3-4-2) were mixed together with the mole ratio of monomer (a4-0-2), monomer (I-1) and monomer (a3-4-2)=50:25:25, and propyleneglycolmonomethylether acetate was added thereto in the amount equal to 1.2 times by mass of the total amount of monomers to obtain a solution. Azobisisobutyronitrile and azobis(2,4-dimethylvaleronitrile) were added as initiators to the solution in the amounts of 0.85% by mole and 2.55% by mole respectively with respect to the total amount of monomers, and the resultant mixture was heated for about 5 hours at 75° C. Then, the obtained reaction mixture was poured into a large amount of a mixture of methanol and ion exchanged water to precipitate a resin. The obtained resin was filtrated. The obtained resin was poured into another methanol to wash. The obtained resin was filtrated to obtain the copolymer having a weight average molecular weight of about 12000 in 80% yield. This resin, which had the structural units of the following formula, was referred to Resin A1-3.

Example 4: Synthesis of Resin A1-4

Monomer (a4-0-2) and monomer (a3-4′-8) were mixed together with the mole ratio of monomer (a4-0-2) and monomer (a3-4′-8)=70:30, and propyleneglycolmonomethylether acetate was added thereto in the amount equal to 1.2 times by mass of the total amount of monomers to obtain a solution. Azobisisobutyronitrile and azobis(2,4-dimethylvaleronitrile) were added as initiators to the solution in the amounts of 0.9% by mole and 2.7% by mole respectively with respect to the total amount of monomers, and the resultant mixture was heated for about 5 hours at 75° C. Then, the obtained reaction mixture was poured into a large amount of a mixture of methanol and ion exchanged water to precipitate a resin. The obtained resin was filtrated. The obtained resin was poured into another methanol to wash. The obtained resin was filtrated to obtain the copolymer having a weight average molecular weight of about 13000 in 78% yield. This resin, which had the structural units of the following formula, was referred to Resin A1-4.

Example 5: Synthesis of Resin A1-5

Monomer (a4-0-12), monomer (I-1) and monomer (a3-4′-8) were mixed together with the mole ratio of monomer (a4-0-12), monomer (I-1) and monomer (a3-4′-8)=50:45:5, and propyleneglycolmonomethylether acetate was added thereto in the amount equal to 1.2 times by mass of the total amount of monomers to obtain a solution. Azobisisobutyronitrile and azobis(2,4-dimethylvaleronitrile) were added as initiators to the solution in the amounts of 1% by mole and 3% by mole respectively with respect to the total amount of monomers, and the resultant mixture was heated for about 5 hours at 75° C. Then, the obtained reaction mixture was poured into a large amount of a mixture of methanol and ion exchanged water to precipitate a resin. The obtained resin was filtrated. The obtained resin was poured into another methanol to wash. The obtained resin was filtrated to obtain the copolymer having a weight average molecular weight of about 8800 in 84% yield. This resin, which had the structural units of the following formula, was referred to Resin A1-5.

Example 6: Synthesis of Resin A1-6

Monomer (a4-0-12), monomer (I-1) and monomer (a3-4′-8) were mixed together with the mole ratio of monomer (a4-0-12), monomer (I-1) and monomer (a3-4′-8)=50:45:5, and propyleneglycolmonomethylether acetate was added thereto in the amount equal to 1.2 times by mass of the total amount of monomers to obtain a solution. Azobisisobutyronitrile and azobis(2,4-dimethylvaleronitrile) were added as initiators to the solution in the amounts of 1% by mole and 3% by mole respectively with respect to the total amount of monomers, and the resultant mixture was heated for about 5 hours at 75° C. Then, the obtained reaction mixture was poured into a large amount of a mixture of methanol and ion exchanged water to precipitate a resin. The obtained resin was filtrated. The obtained resin was poured into another methanol to wash. The obtained resin was filtrated to obtain the copolymer having a weight average molecular weight of about 9200 in 78% yield. This resin, which had the structural units of the following formula, was referred to Resin A1-6.

Example 7: Synthesis of Resin A1-7

Monomer (a4-0-12), monomer (1-1) and monomer (a3-4′-8) were mixed together with the mole ratio of monomer (a4-0-12), monomer (I-1) and monomer (a3-4′-8)=50:45:5, and propyleneglycolmonomethylether acetate was added thereto in the amount equal to 1.2 times by mass of the total amount of monomers to obtain a solution. Azobisisobutyronitrile and azobis(2,4-dimethylvaleronitrile) were added as initiators to the solution in the amounts of 1% by mole and 3% by mole respectively with respect to the total amount of monomers, and the resultant mixture was heated for about 5 hours at 75° C. Then, the obtained reaction mixture reaction mixture was poured into a large amount of a mixture of methanol and ion exchanged water to precipitate a resin. The obtained resin was filtrated. The obtained resin was poured into another methanol to wash. The obtained resin was filtrated to obtain the copolymer having a weight average molecular weight of about 9200 in 82% yield. This resin, which had the structural units of the following formula, was referred to Resin A 1-7.

Example 8: Synthesis of Resin A1-8

Monomer (a4-0-12), monomer (I-1) and monomer (a3-4′-7) were mixed together with the mole ratio of monomer (a4-0-12, monomer (1-1) and monomer (a3-4′-7)=50:45:5, and propyleneglycolmonomethylether acetate was added thereto in the amount equal to 1.2 times by mass of the total amount of monomers to obtain a solution. Azobisisobutyronitrile and azobis(2,4-dimethylvaleronitrile) were added as initiators to the solution in the amounts of 1% by mole and 3% by mole respectively with respect to the total amount of monomers, and the resultant mixture was heated for about 5 hours at 75° C. Then, the obtained reaction mixture was poured into a large amount of a mixture of methanol and ion exchanged water to precipitate a resin. The obtained resin was filtrated. The obtained resin was poured into another methanol to wash. The obtained resin was filtrated to obtain the copolymer having a weight average molecular weight of about 9400 in 77% yield. This resin, which had the structural units of the following formula, was referred to Resin A1-8.

Synthesis Example 4: Synthesis of Resin A2-1

Monomer (a1-1-3), monomer (a1-2-9), monomer (a2-1-3) and monomer (a3-4-2) were mixed together with a mole ratio of monomer (a1-1-3), monomer (a1-2-9), monomer (a2-1-3) and monomer (a3-4-2)=45:14:2.5:38.5, and propyleneglycolmonomethylether acetate was added thereto in the amount equal to 1.5 times by mass of the total amount of monomers to obtain a solution. Azobisisobutyronitrile and azobis(2,4-dimethylvaleronitrile) were added as initiators to the solution in the amounts of 1% by mole and 3% by mole respectively with respect to the total amount of monomers, and the resultant mixture was heated for about 5 hours at 73° C. Then, the obtained reaction mixture was poured into a large amount of a mixture of methanol and water to precipitate a resin. The obtained resin was filtrated. The obtained resin was dissolved in another propyleneglycolmonomethylether acetate to obtain a solution, and the solution was poured into a large amount of a mixture of methanol and water to precipitate the resin. The obtained resin was filtrated. These operations were repeated twice to obtain the copolymer having a weight average molecular weight of about 7600 in 68% yield. This resin, which had the structural units of the following formulae, was referred to Resin A2-1.

Synthesis Example 5: Synthesis of Resin A2-2

Monomer (a1-1-3), monomer (a1-2-9), monomer (a2-1-1) and monomer (a3-4-2) were mixed together with a mole ratio of monomer (a1-1-3), monomer (a1-2-9), monomer (a2-1-1) and monomer (a3-4-2)=45:14:2.5:38.5, and propyleneglycolmonomethylether acetate was added thereto in the amount equal to 1.5 times by mass of the total amount of monomers to obtain a solution. Azobisisobutyronitrile and azobis(2,4-dimethylvaleronitrile) were added as initiators to the solution in the amounts of 1% by mole and 3% by mole respectively with respect to the total amount of monomers, and the resultant mixture was heated for about 5 hours at 73° C. Then, the obtained reaction mixture was poured into a large amount of a mixture of methanol and water to precipitate a resin. The obtained resin was filtrated. The obtained resin was dissolved in another propyleneglycolmonomethylether acetate to obtain a solution, and the solution was poured into a large amount of a mixture of methanol and water to precipitate the resin. The obtained resin was filtrated. These operations were repeated twice to obtain the copolymer having a weight average molecular weight of about 7900 in 67% yield. This resin, which had the structural units of the following formulae, was referred to Resin A2-2.

Synthesis Example 6: Synthesis of Resin A1X-1

Monomer (a4-0-1) and monomer (I-2) were mixed together with a mole ratio of monomer (a4-0-1) and monomer (I-2)=50:50, and propyleneglycolmonomethylether acetate was added thereto in the amount equal to 1.2 times by mass of the total amount of monomers to obtain a solution. Azobisisobutyronitrile and azobis(2,4-dimethylvaleronitrile) were added as initiators to the solution in the amounts of 0.9% by mole and 2.7% by mole respectively with respect to the total amount of monomers, and the resultant mixture was heated for about 5 hours at 75° C. The obtained reaction mixture was poured into a large amount of a mixture of methanol and ion exchanged water to precipitate a resin. The obtained resin was filtrated. The obtained resin was poured into another methanol to wash. The obtained resin was filtrated to obtain the copolymer having a weight average molecular weight of about 12000 in 90% yield. This resin, which had the structural units of the following formula, was referred to Resin A1X-1.

Synthesis Example 7: Synthesis of Resin A1X-2

Monomer (a4-0-2) and monomer (a3-1-1) were mixed together with the mole ratio of monomer (a4-0-2) and monomer (a3-1-1)=31:69, and propyleneglycolmonomethylether acetate was added thereto in the amount equal to 1.5 times by mass of the total amount of monomers to obtain a solution. Azobisisobutyronitrile and azobis(2,4-dimethylvaleronitrile) were added as initiators to the solution in the amounts of 1% by mole and 3% by mole respectively with respect to the total amount of monomers, and the resultant mixture was heated for about 5 hours at 75° C. Then, the obtained reaction mixture was poured into a large amount of a mixture of methanol and ion exchanged water to precipitate a resin. The obtained resin was filtrated. The obtained resin was poured into another methanol to wash. The obtained resin was filtrated to obtain the copolymer having a weight average molecular weight of about 7500 in 75% yield. This resin, which had the structural units of the following formula, was referred to Resin A1X-2.

Synthesis Example 8: Synthesis of Resin A1X-3

Monomer (a4-0-2) and monomer (a3-2-1x) were mixed together with the mole ratio of monomer (a4-0-2) and monomer (a3-2-1x)=31:69, and propyleneglycolmonomethylether acetate was added thereto in the amount equal to 1.5 times by mass of the total amount of monomers to obtain a solution. Azobisisobutyronitrile and azobis(2,4-dimethylvaleronitrile) were added as initiators to the solution in the amounts of 1% by mole and 3% by mole respectively with respect to the total amount of monomers, and the resultant mixture was heated for about 5 hours at 75° C. Then, the obtained reaction mixture was poured into a large amount of a mixture of methanol and ion exchanged water to precipitate a resin. The obtained resin was filtrated. The obtained resin was poured into another methanol to wash. The obtained resin was filtrated to obtain the copolymer having a weight average molecular weight of about 7700 in 70% yield. This resin, which had the structural units of the following formula, was referred to Resin A1X-3.

(Preparing Resist Compositions)

Resist compositions were prepared by mixing and dissolving each of the components shown in Table 1, and then filtrating through a fluoro resin filter having 0.2 μm pore diameter. The obtained resist compositions were stored for 3 weeks at 30° C. Then, the properties of the resist compositions were evaluated.

TABLE 1 Weakly Acidic Inner PB/PEB Resin Acid Generator Salt (D) (° C./ Resist Comp. (parts) (B) (parts) (parts) ° C.) Composition 1 A1-1/A2-1 = B1-21/B1-22 = D1 = 0.28 90/85 0.7/10 0.9/0.4 Composition 2 A1-1/A2-1 = B1-5/B1-22 = D1 = 0.28 90/85 0.7/10 0.4/0.4 Composition 3 A1-2/A2-1 = B1-21/B1-22 = D1 = 0.28 90/85 0.7/10 0.9/0.4 Composition 4 A1-3/A2-1 = B1-21/B1-22 = D1 = 0.28 90/85 0.7/10 0.9/0.4 Composition 5 A1-4/A2-1 = B1-21/B1-22 = D1 = 0.28 90/85 0.7/10 0.9/0.4 Composition 6 A1-5/A2-1 = B1-21/B1-22 = D1 = 0.28 90/85 0.7/10 0.9/0.4 Composition 7 A1-6/A2-1 = B1-21/B1-22 = D1 = 0.28 90/85 0.7/10 0.9/0.4 Composition 8 A1-7/A2-1 = B1-21/B1-22 = D1 = 0.28 90/85 0.7/10 0.9/0.4 Composition 9 A1-8/A2-1 = B1-21/B1-22 = D1 = 0.28 90/85 0.7/10 0.9/0.4 Composition 10 A1-5/A2-2 = B1-21/B1-22 = D1 = 0.28 90/85 0.7/10 0.9/0.4 Composition 11 A1-6/A2-2 = B1-21/B1-22 = D1 = 0.28 90/85 0.7/10 0.9/0.4 Composition 12 A1-7/A2-2 = B1-21/B1-22 = D1 = 0.28 90/85 0.7/10 0.9/0.4 Composition 13 A1-8/A2-2 = B1-21/B1-22 = D1 = 0.28 90/85 0.7/10 0.9/0.4 Comparative A1X-1/A2-1 = B1-21/B1-22 = D1 = 0.28 90/85 Comp. 1 0.7/10 0.9/0.4 Comparative A1X-2/A2-1 = B1-21/B1-22 = D1 = 0.28 90/85 Comp. 2 0.7/10 0.9/0.4 Comparative A1X-3/A2-1 = B1-21/B1-22 = D1 = 0.28 90/85 Comp. 3 0.7/10 0.9/0.4 <Resin>

Resins: Resins A1-1 to A1-8, A2-1, A2-2, A1X-1 and A1X-2, each prepared by the method as described above

<Acid Generator (B)>

B1-5: Salt represented by the formula (B1-5)

B1-21: Salt represented by the formula (B1-21)

B1-22: Salt represented by the formula (B1-22)

<Weakly Acidic Inner Salt (D)>

D1: Compound as follow, a product of Tokyo Chemical Industry Co., LTD

<Solvent for Resist Compositions>

Propyleneglycolmonomethylether acetate 265 parts  Propyleneglycolmonomethyl ether 20 parts 2-Heptanone 20 parts γ-butyrolactone 3.5 parts  <Evaluation of Resist Compositions>

A composition for an organic antireflective film (“ARC-29”, by Nissan Chemical Co. Ltd.) was applied onto 12-inch silicon wafer and baked for 60 seconds at 205° C. to form a 78 nm thick organic antireflective film.

One of the resist compositions was then applied thereon by spin coating in such a manner that the thickness of the film after drying (pre-baking) became 100 nm.

The obtained wafer was then pre-baked for 60 sec on a direct hot plate at the temperature given in the “PB” column in Table 1.

On the wafers on which the composition layer had thus been formed, the film was then exposed through a mask for forming trench patterns (pitch 120 nm/trench width 40 nm) with changing exposure quantity stepwise, by an ArF excimer laser stepper for liquid-immersion lithography (“XT:1900Gi” by ASML Ltd.: NA=1.35, Annular σout=0.9 σin=0.7 XY-pol.). Ultrapure water was used for medium of liquid-immersion.

After the exposure, post-exposure baking was carried out for 60 seconds at the temperature given in the “PEB” column in Table 1.

Then, development was carried out with butyl acetate (a product of Tokyo Chemical Industry Co., LTD) at 23° C. for 20 seconds in the manner of dynamic dispensing method to obtain negative resist patterns.

Effective sensitivity was represented as the exposure quantity at which the resist pattern with 40 nm trench width was obtained.

(Line Edge Roughness (LER) Evaluation)

The wall surface of the resist pattern following the lithography process was observed using a scanning electron microscope.

The “∘” was given when the irregularity in wall surface has a roughness width of 3 nm or less.

The “x” was given when the irregularity in wall surface has a roughness width of more than 3 nm.

Table 2 illustrates the results thereof. The figures in parentheses mean roughness width values (nm).

(Evaluation of Defects)

Negative resist patterns were produced in the same manner as described above, except that the film was exposed with exposure quantity at which the ratio of the widths between the line and space became 1:1, using an ArF excimer laser stepper for immersion lithography (“XT:1900Gi” by ASML Ltd.: NA=1.35, Annular σ_(out)=0.85 σ_(in)=0.65 XY-pol.) and a mask for making a 1:1 line and space patterns (pitch 80 nm, line width 40 nm).

Thereafter, the number of defects was counted using a defect inspection apparatus (KLA-2360, KLA-Tencor Co. Ltd.). Table 2 illustrates the results thereof.

TABLE 2 Resist Composition LER Defects Ex. 9 Composition 1 ∘ (2.86) 320 Ex. 10 Composition 2 ∘ (2.89) 310 Ex. 11 Composition 3 ∘ (2.79) 260 Ex. 12 Composition 4 ∘ (2.83) 280 Ex. 13 Composition 5 ∘ (2.85) 380 Ex. 14 Composition 6 ∘ (2.76) 270 Ex. 15 Composition 7 ∘ (2.88) 290 Ex. 16 Composition 8 ∘ (2.90) 300 Ex. 17 Composition 9 ∘ (2.98) 330 Ex. 18 Composition 10 ∘ (2.72) 240 Ex. 19 Composition 11 ∘ (2.84) 280 Ex. 20 Composition 12 ∘ (2.89) 290 Ex. 21 Composition 13 ∘ (2.95) 300 Comparative Ex. 1 Comparative Comp. 1 x (3.01) 980 Comparative Ex. 2 Comparative Comp. 2 x (3.22) 1260 Comparative Ex. 3 Comparative Comp. 3 x (3.16) 1120

The resist composition of the disclosure shows excellent preservation stability and can provide resist patterns with less excellent line edge roughness (LER) and reduced defects. Therefore, the present resist composition can be used for semiconductor microfabrication. 

What is claimed is:
 1. A resist composition comprising (A1) a resin which comprises a structural unit represented by formula (a4):

wherein R³ represents a hydrogen atom or a methyl group, and R⁴ represents a C₁ to C₂₄ fluorinated alkyl group, and a structural unit having an adamantane lactone group represented by formula (a3-4I):

wherein R⁵ represents a hydrogen atom, a halogen atom, or a C₁ to C₆ alkyl group that may have a fluorine atom, A⁴ represents an oxygen atom or an NH group, and A⁵ represents *-A²-O—, *-A²-CO—O—, *-A²-CO—O-A³-CO—O— or *-A²-O—CO-A³-O— in which A² and A³ each independently represent a C₁ to C₆ alkanediyl group, and the resin having no acid-labile group, (A2) a resin having an acid-labile group, and an acid generator.
 2. The resist composition according to claim 1, wherein the structural unit having an adamantane lactone group is a structural unit represented by formula (a3-4′):

wherein R⁵ represents a hydrogen atom, a halogen atom, or a C₁ to C₆ alkyl group that may have a fluorine atom, A¹ represents *-A²-O—, *-A²-CO—O—, *-A²-CO—O-A³-CO—O— or *-A²-O—CO-A³-O— where * represents a binding site to an oxygen atom, and A² and A³ are as defined in claim
 1. 3. The resist composition according to claim 2, wherein the structural unit represented by the formula (a3-4′) has an adamantane lactone group represented by formula (a3-4II-a) or formula (a3-4II-b):

wherein * represents a binding site to A¹.
 4. The resist composition according to claim 1, wherein the resin (A2) comprises a structural unit selected from the group consisting of a structural unit represented by formula (a1-1) and a structural unit represented by formula (a1-2):

wherein L^(a1) and L^(a2) independently represent —O— or *—O—(CH₂)_(k1)—CO—O—, k1 represents an integer of 1 to 7, represents a binding site to —CO—, R^(a4) and R^(a5) each independently represent a hydrogen atom or a methyl group, R^(a6) and R^(a7) each independently represent a C₁ to C₈ alkyl group, a C₃ to C₁₈ alicyclic hydrocarbon group or a combination thereof, m1 represents an integer of 0 to 14, n1 represents an integer of 0 to 10, and n1′ represents an integer of 0 to
 3. 5. The resist composition according to claim 4, wherein the resin (A2) comprises a structural unit represented by formula (a1-1) and a structural unit represented by formula (a1-2).
 6. A method for producing a resist pattern comprising steps (1) to (5); (1) applying the resist composition according to claim 1 onto a substrate; (2) drying the applied composition to form a composition layer; (3) exposing the composition layer; (4) heating the exposed composition layer, and (5) developing the heated composition layer.
 7. A resin comprising a structural unit represented by formula (a4):

wherein R³ represents a hydrogen atom or a methyl group, and R⁴ represents a C₁ to C₂₄ fluorinated alkyl group, and a structural unit having an adamantane lactone group represented by formula (a3-4I):

wherein R⁵ represents a hydrogen atom, a halogen atom, or a C₁ to C₆ alkyl group that may have a fluorine atom, A⁴ represents an oxygen atom or an NH group, and A⁵ represents *-A²-O—, *-A²-CO—O—, *-A²-CO—O-A³-CO—O— or *-A²-O—CO-A³-O— in which A² and A³ each independently represent a C₁ to C₆ alkanediyl group, and the resin having no acid-labile group.
 8. The resin according to claim 7, wherein the structural unit having an adamantane lactone group is a structural unit represented by formula (a3-4′):

wherein R⁵ represents a hydrogen atom, a halogen atom, or a C₁ to C₆ alkyl group that may have a fluorine atom, A¹ represents *-A²-O—, *-A²-CO—O—, *-A²-CO—O-A³-CO—O— or *-A²-O—CO-A³-O— where * represents a binding site to an oxygen atom, and A² and A³ are as defined in claim
 7. 